ADF : Working with LOV Switcher

Hello all,

This is a very basic post on LOV switcher implementation.
First , some background information about it.

First we need to understand what happens when a Lov is added to an attribute in ViewObject.

When we add a Lov to an attribute in a ViewObject, a property is added to the attribute

  LOVName="LOV_Name"

and a viewObject instance of the Lov is added to the viewObject. You can see it in the viewAccesors tab to ViewObject. And an entry of list binding is made in the viewObject to represent attribute mapping for the LOV viewObject.
So the question is how the Framework determines if which LOV is added to the attribute,  at runtime ?
At first Framework looks for the property LOVName of the attrribute of the ViewObject then looks for the List binding of the LOV name.

So inorder to switch the LOV on an attribute we just have to change the value of the LOVName in the attribute.Means we need to give it the name of the lov whichever we want to display. LOV switcher basically does the same thing.

So here is an example for the same.
Here I am creating a transient attribute in a Temporary viewObject made from dual and on this attribute we will switch Departments and Employees LOV. I have also created two viewObjects of Department and Employees to use them to make LOV.

First we have to create a Temporary ViewObject with a transient attribute.
Then we will create a transient attribute in which we will put the name of the LOV and then use it will as name of the LOV which needs to be selected.
Here I am naming it as 'LovNameTrans'.

Then we will create two lov on attribute 'LovAttributeTrans'.
Here I have used 'LOVDept' as the name of the LOV.

And again am creating second LOV on the same attribute and named it 'LOVEmp'.

Now the LOV part is over now we have make the switching arrangement.
So now in the 'List of Values Switcher' select the attribute 'LovNameTrans' which will provide the name of the LOV to be switched.

Now create a page and drop the attributes.For assigning values to the 'LovNameTrans' attribute i have created a radio group with static list containing the LOV names.

Make sure the attribute containing the name of teh LOv have the autosubmit property as true on the page as if the value is not submitted then LOV will not be shown. And also use proper partil triggers.

Now run the page. On selecting LOVDept

On selecting LOVDept

Here is the sample workspace used, you can download it from here :LovSwitcherApp

How to scroll a table in oracle ADF with large number of rows in database (>100K rows)?? Resolved!!

Hello ,

There are times in development when we have to show tables with large number of rows to user on the Page. ADF table contains very good property of Scroll which fetches the data from the database when the user scrolls in the table.
This works well when the number of rows in the table is less i.e we can say around 4-5000 without much problem. But the problem begins when we have Thousands or Lacks of rows in the table.

On the default settings when you scroll to the 10000th row then the table fetches all the data upto the 10000th row and then shows the results in the table. When the table starts fetching the 10000 rows in the memory then it takes time , here comes the problem. So if we can reduce this time then we can solve the problem.

Before solving the problem first we need to know why this problem comes into picture.
The problem is that when the user scrolls on the 10000th row, the framework start loading all the 10000 rows in the memory to show on the page, and this takes time.
For avoiding this problem we can customize the setting in ViewObject tuning section.
Go to the Tuning section of any ViewObject, you will see following options .

We have to focus on following properties.

# Retrieve rows from the database : It can be set to :

1. All Rows (All the rows will be fetch at a time, when the number of rows are large then it takes so much time.)
2. Only upto row number (Makes sure that only the rows upto the given number are fetched)
3.  in batches of (It defines the number of rows fetched in one roundTrip to database. Its value depends on the use case but I this case we keep it to n+1, where n is the number of rows to be shown on the page. )

# Access Mode (This is the property to be concerned)

1. Scrollable : when acess mode is scrollable it means as the user scrolls all the rows upto which user have scrolled will be loaded in the memory before it is shown on the page.
2. Page Ranging : when the access mode is Page Ranging then when the user scrolls upto some row then only the rows that need to be displayed currently are loaded in to the memory. Let us take an example. Suppose the user scrolls to 10000th row then the RANGE containing row number 10000 will only get loaded into the memory.

So less time needed to load the rows hence table loads faster

# Range size 

It defines the range, We keep the range size to n+1 where n is the number of rows that the user needs to show on the page. 

Range size basically means the number of rows that will be loaded from the viewObject cache to the binding. This is kept to n+1 because if the we don't want more than one round trip to database as if the range size increases the fetch size then an another roundTrip to fetch values in issued.

Also keep the range of the table in sync with the range size of of the table, it helps. 

ADF : Calling Action from ActionEvent Programmatically

Hello all,

During the development sometimes we need to call the "Action" within "ActionListner". That would be when you have to perform a calculation in ActionListner and then decide whether to navigate or not.

Here is the code for doing so

If you have any questions feel free to ask.

ADF : Filtering ListOfValues Effectively, Best way to filter an LOV

Hello all,

This is an initial level post, but still thinks can get tricky at times, so i thought of sharing this.

Here I will try to demonstrate how we can filter the values of an LOV effectively.
First we need to know about what happens when an LOV is added on an attribute in a viewObject.

When a LOV is added on an attribute then an instance of the viewObject ( which is used for creating LOV ) is created and that is added to the attribute as an LOV. This instance is attached to the parent viewObject.
Let us take an example,
Suppose we have to show departments in place of department Id in EmployeeViewObject made from Employees Table.
For doing so we will have create a viewObject containing DeptId and DepartmentName, we can name it LovDeptVO. Then we will select the departmentId field in EmployeeViewObject and add LOV and select LovDeptVO viewObject and do attribute mapping , at this time an instance of viewObject LovDeptVO is created and added to EmployeeViewObject. And then you can view the instance of the lov in viewAccessors Tab of EmployeeViewObject.

So now we come to filtering the LOV on somevalues.

There are two cases :

1. Filtering LOV with the attribute present in the same ViewObject.
We have to create a viewCriteria in the lov ViewObject and pass values to bind variables from the viewObject which contains the LOV.
Let us take an example ;

I have created an ADF Applcation with HR Schema.

Then created a temprory viewObject containing two attributes departmentId and EmployeeId.

Then we have to create EmployeeViewObject to make LOV from it.

Now go to Query Tab and create a viewCriteria filtering the LOVEmployeeVo with DeptId. So now LOV viewObject is also complete.

Now we have to make LOV in the EmployeeId in TempVO. Select the EmployeeId attribute go to ListOfValues section and add an lov by clicking add button.

Now we have to pass the selected DepartmentID to LOV so that i can be filtered. So go to the viewAccessors tab in TempVO. You will see the LOV instance there.

Click edit and pass the values. Drag the available viewCriteia to the left and pass the value to the bindVariable.

New Create a page and drop the TempVO as a form. Set Autosubmit value of DepartmentId field to true. And add partial trigger on EmployeeId attribute to refresh the LOV when value of Department changes.

2. Filtering LOV with the attribute present outside the ViewOject i.e. filtering LOV from outside.

So in the above case we had to filter the lov from the attribute from the ViewObject containing Lov, i mean EmployeeId and DepartmentId both fields were in the same ViewObject. How will we filter when we have to filter the LOV on the basis of value coming from a diffferent ViewObject.

For this purpose i created a text field on the page and created a button to filter the LOV.

For that I have created a method in AmImpl and called it in the bean by adding it to client interface.

Method in AMImpl .

And In Bean I have called the Method in AM

On Running the application

When DepartmentId is entered as 10 and filterLov button is clicked

You can download the sample Application here : LovTestApp.rar

ADF : Programmatic ViewObjects in ADF, Populating programmatic viewObject with an ArrayList

Hello all,

Today I am going to demonstrate about how to make programmatic viewObject in ADF.
There are basically 4 types of viewObjects.

1. ViewObjects based on Entity.
2. ViewObjects based on SqlQuery (also called Readonly viewObject)
3. Static viewObjects (contains fix now of rows)
4. Programmatic viewObjects (Programmatic viewObjects are viewObjects that are not populated from an sql query).

For understanding  the working of programmatic viewObjects, you must first understand the lifecycle of a viewObject. You need to know what methods are called when a viewObject is executed. Here is the sequence of methods that are called when a viewObject is executed.

LIFECYCLE

When a viewObject is called the following methods are executed in the given sequence. 

• At first when the viewObject is first executed the method first called in the ViewObjectImpl is
  executeQueryForCollection(Object qc, Object[] params, int noUserParams)
  This method executes the Database Query in the viewObject and then calls the next method.


• After executeQueryForCollection is executed then method hasNextForCollection(Object qc) is called. This method checks if the collection returned have a row or not. If hasNextForCollection(Object qc) returns True then the next method of the lifeCycle is called which converts the row to ADF understandable form i.e. into ViewObjectRowImpl from.


• So when method hasNextForCollection retuns true then method createRowFromResultSet(Object qc, ResultSet resultSet) is called and this method converts the row into ADF understandable form.


• This goes on until all the rows are covered and there is no rows left in collection. When there are no rows in the collection then the method hasNextForCollection returns false .


• Then method setFetchCompleteForCollection(java.lang.Object qc,boolean val) is called and it sets the flag for fetch completion. This indicates that the rows from the collection are fetched.

- See more at: http://adfjavacodes.blogspot.in/2013/12/how-viewobjects-get-executed.html#sthash.whg7AwM9.dpuf

Now create an ADF Application and create a programmatic viewobject

Then press next and define attributes for the viewObject

Generate the following java classes

Click Finish.

Now we have made the viewObject. We will have to override the lifeCycle methods. Here is the code that I have used for this viewObject.

package programmaticvotestapp.model.views;

import java.sql.ResultSet;

import java.util.ArrayList;

import oracle.jbo.Row;
import oracle.jbo.server.ViewObjectImpl;
import oracle.jbo.server.ViewRowImpl;
import oracle.jbo.server.ViewRowSetImpl;

import programmaticvotestapp.model.EmpDC;
// ---------------------------------------------------------------------
// ---    File generated by Oracle ADF Business Components Design Time.
// ---    Wed Apr 09 14:28:40 IST 2014
// ---    Custom code may be added to this class.
// ---    Warning: Do not modify method signatures of generated methods.
// ---------------------------------------------------------------------
public class ProgrammaticVOImpl extends ViewObjectImpl {
    private ArrayList<EmpDC> empList = new ArrayList<EmpDC>(); 
    /**
     * This is the default constructor (do not remove).
     */
    public ProgrammaticVOImpl() {
    }

    /**
     * executeQueryForCollection - overridden for custom java data source support.
     * This method is executed at first.
     * So in this method we need to load our data source . 
     * In simple words initialize the list
     */
    protected void executeQueryForCollection(Object qc, Object[] params, int noUserParams) {
        // Populate the list for the firstTime
        populateArrayList();
        //To set the initial position for fetch to start
        setFetchPosition(qc,0);
        super.executeQueryForCollection(qc, params, noUserParams);
    }

    /**
     * hasNextForCollection - overridden for custom java data source support.
     * This method is called after executeQueryForCollection to check if any row exist in the datasource or not.
     * When returned true, createRowFromResultSet is called and a new row from the rowset is created.
     */
    protected boolean hasNextForCollection(Object qc) {
        return getFetchPosition(qc) < empList.size();
    }

    /**
     * createRowFromResultSet - overridden for custom java data source support.
     * creates a newRow and adds it to viewObject
     */
    protected ViewRowImpl createRowFromResultSet(Object qc, ResultSet resultSet) {
        int fetchPosition = getFetchPosition(qc);
        System.out.println("Fetch Position is : "+fetchPosition);
        ViewRowImpl newRow = (ViewRowImpl)createNewRowForCollection(qc);
        EmpDC c = empList.get(fetchPosition);
        // Setting value in the new row which is created.
        newRow.setAttribute("EmpId", c.getEmpId());
        newRow.setAttribute("EmpName", c.getEmpName());
        newRow.setAttribute("Salary", c.getSalary());
        // Updating the fetch Position
        setFetchPosition(qc, fetchPosition+1);
        
        return newRow;
    }

    /**
     * getQueryHitCount - overridden for custom java data source support.
     */
    public long getQueryHitCount(ViewRowSetImpl viewRowSet) {
        long value = empList.size();
        return value;
    }
    /**
         * Method to set the new fetch position
         * @param rowset
         * @param position
         * To set the position on the nextRecord to fetch i.e. next record of arrayList
         */
        private void setFetchPosition(Object rowset, int position) {
            if (position == empList.size()-1) {
                setFetchCompleteForCollection(rowset, true);
            }
            setUserDataForCollection(rowset, new Integer(position));
        
    }
    /**
         * Method to get the current fetch position
         * @param rowset
         * @return
         * 
         * This method gets the fetchPosition to fetch the row from the arrayList to retrieve the data
         */
        private int getFetchPosition(Object rowset) {
            int value = ((Integer)getUserDataForCollection(rowset)).intValue();
            return value;
        }
    
    public void populateArrayList(){
        empList.clear();
        empList.add(new EmpDC(1,1100,new StringBuffer("First Employee")));
        empList.add(new EmpDC(2,2100,new StringBuffer("Second Employee")));
        empList.add(new EmpDC(3,1300,new StringBuffer("Third Employee")));
        empList.add(new EmpDC(4,1700,new StringBuffer("Fourth Employee")));
        empList.add(new EmpDC(5,1200,new StringBuffer("Fifth Employee")));
        empList.add(new EmpDC(6,5100,new StringBuffer("Sixth Employee")));
        empList.add(new EmpDC(7,1900,new StringBuffer("Seventh Employee")));
        empList.add(new EmpDC(8,1200,new StringBuffer("Eight Employee")));
        empList.add(new EmpDC(9,1200,new StringBuffer("Ninth Employee")));
        empList.add(new EmpDC(10,1100,new StringBuffer("Tenth Employee")));
    }
}

on running the application you can see

You can download the sample application here ProgrammaticVoApp

Likewise you can use other datasources to populate the programmatic viewObject. The above model shows a very simple implementation, use cases can be much complex.


References :
1 .http://huysmansitt.blogspot.in/2012/08/adf-programmatical-views-made-simple.html?showComment=1397033254692#c2288712975950397947
2 .http://adfjavacodes.blogspot.in/2013/12/how-viewobjects-get-executed.html

ADF : Making three level dependent LOV (List Of Values)

Hello all,

During the development we often come across a scenario in which we need to filter the List Of Values dependent on other List Of Values. Suppose you want only the cities of the selected country.

Here am about to show how we can make a three level dependent ListOfValues.
I will make a LOV which the user will select a location from locationLOV , then the other departmentLOV will show the department of the selected location, then the user will select a department and the employeeLOV will show the Employees of the selected department.

So, I have created an ADF application and made a connection to HR Schema. Also created three viewObject LovDepartmentVO,LovLocationsVO and LovEmployeeVO to make LOV's.

Now our main purpose is to filter the department on the basis of locations and employees on the basis of department.

For that we have to create a viewCritria in DepartmentsVo to filter departments on the basis of locations.

And then create view criteria for EmployeesVO.

Now we have viewObjects for LOV ready, we need to make a viewObject on whose attributes we will put these lovs.

So here I am creating a query from dual.
And then add three transient attributes as location , department and employees.
Make sure that property "updatable" is true.

Select locationsTrans and go to List of Values and add the lov by selecting LovLocationsVO.
Select departmentTrans and make a lov from lovDepartmentsVO.
Now go to view Accessors tab of the TemporaryVO you will see the lovs added to temporaryVO, now select the lovDepartment and click on edit button.

Select the viewCritera and in the bind value parameters select locationsTrans as value. This will filter the departments Lov on the basis of selecetd location.

Now add the lov on employeesTrans too and then go to viewAccessors select and mapp the bindVarible value to departmentTrans.

Now create am Applicaiton Module and add temporaryVo to AM and create a page and drag all the three attributes in the page and run the application.

Run the page and Select LocationTrans as London, then you will see DepartmentTrans filtered and you will see only 'Humar Resource' department in the lov as it resides in London. And in EmployeeTrans you will see Employees of Selected  department.

Make sure that the all the attribute have their autosubmit attribute to 'true' and attributes are partial trigged on basis of the source.

And the most important thing is that this technique will work on when the three attributes are on the same viewObject.. like in this case is the TemporaryVO.

You can Download the sample from here DependentLovTest.jar

If you have any questions regarding this, feel free to ask.

Validator in oracle ADF, Using af:attribute to make validation easy.

Hello all,

This post I will try to focus on how we can make validations in an editable table more effectively.

So what would we do if we have two attributes in a row in a table and we need to validate one on the basis of the other?

The answer is simple.

• We will get the instance of the viewObject 
• Then get the current row 
• Then we will get the attribute with which we need to compare and then we will compare and check the validation.

This process is fine, but i have a more easy and effective way to do so.

I have created a Transient attribute in EmployeeVO where the newSalary of the Employee is to be entered. We have to make sure that the new Salary is greater than old salary.

Drag the EmployeeVO into the page. Then add an af:attribute component in the inputText of newSalaryTrans . Give attribute name and a value here i have used 'oldSal' and assigned with value of old Salary i.e. #{row.Salary}.

Now we need to implement the validation and for that I created a Validator on the NewSalaryTrans field.

In the bean I have used the code given below :

    public void newSalaryVAL(FacesContext facesContext, UIComponent uIComponent, Object object) {
        Object val = uIComponent.getAttributes().get("oldSal");
        System.out.println("New Sal is  : "+object+" Old Sal is  : "+val);
        if(val != null){
            BigDecimal oldVal = (BigDecimal)val;
            BigDecimal newVal = (BigDecimal)object;
             if(oldVal.compareTo(newVal) >=0 ){
                throw new ValidatorException(new FacesMessage("New Salary Cannnot be less than Old Salary!"));
            }
        }
    }

On putting less value in newSalaryTrans

Here is the sample example : NewValidatorTestApp

ADF : af:table or adf form or adf page taking too much time to load

During the development sometimes we come across this problem. In our case we had a table on a page and it was taking too much time to load, even though there were only one row in the database table but then also it was taking more than enough time to load. After the analysing the problem finally we were able to solved the problem.

The main problem was with the List of Values with SingleSelection which was inserted in the table. In a column we had to show the name in place of the id, so the developer created a List of Values in the viewObject and put it in the table on page. At first it was working fine but later as the number of rows grown in the List of values the list started taking time to load.

The main cause was the number of rows in the list of values. Single selection list of values matches the id with the value and shows values, so inorder to map it needs all the rows, so whenever the table was being load the ListOfValues started to fetch all the rows, and as the number of rows was too much so abviously it was taking too much time. So, we had to replace the list of values but we also had to show the name in place of id. 

So there are many ways to do that : 

1. We can include the name that we have to display in the query of the table itself, because of which we can simply display it in a column.

2. Otherwise we have to use a viewobject with query that returns a less number of rows and better if it returns one row with the id and DisplayName. 

Suppose we have to show Department Name in place of department id in Employees Table. The query will be something like this : SELECT DEPARTMENT_NAME FROM DEPARTMENTS WHERE DEPARTMENT_ID = :DeptIdBind

And then we need to show the display name so we created a transient attribute.

Then in the getter of the transient attribute, get the viewObject and pass the bindVariables and execute the query. The query will return a row and then we can fetch the name from the view object and show it by returning it.

There is a disadvantage of using this method, as the query is executed for all the rows fetched in the table. But page load problem will be solved. 

This may depend on the use case.  For us both worked well.

I will suggest never to use SingleSelection List of Values that contains large number of rows in the page. Not even on the adf form. Because due to that it will take too much time to load.

Thanks for reading. If you have any question, Please feel free to ask.

ADF : Alternate of Current Row Selection In af:table | Using f:attribute in ADF

Today am about to show how we can get the value of the selected row from a table without using the RowSelection property of the table.

This came to my mind when I was working on an editable table on a PopUp. And the scenario was that when the user clicks on a link or button in the table then an another table on a new popup need to be shown. The other thing was that both the tables contains large number of rows.

The problem was when we were selecting the current row in table the Framework was trying to make the selected row as current, because of which it was refreshing the table.So every time I select a row the whole table was being refreshed to set selected row as current.

So I tried out some other way to to the same.

Here is the sample Application .

I have created a Application with HR Schema with Employee and Department tables. On the page I have dropped two popUps, First for department table and second for employee table.

Drag the Department table on the popup and set rowSelection to none.

Put a Command button the department table. And add an f:attribute in the commandButton and give it a name and value as department id.

Here I have used Department Id as it is the key to department table like wise you can use user primary key as key. And then you can find the row from the key.

Then on other popup drag the employee table.

In the employees table create a viewCriteria on DepartmentId.

On click on OpenEmployee button, I have used a method to get the attibute.

    public void openEmpACTION(ActionEvent actionEvent) {
        RichCommandButton ob = (RichCommandButton)actionEvent.getSource();
        Integer dept = (Integer)ob.getAttributes().get("DeptId");
        System.out.println("Dept id is : "+dept);
        OperationBinding binding = getBindings().getOperationBinding("setDeptIdInEmployee");
        binding.getParamsMap().put("deptId", dept);
        binding.execute();
        showPopup(popEmp, true);
        //   setDeptIdInEmployee
    }
    /**Method to get Binding Container*/
    public BindingContainer getBindings() {
        return BindingContext.getCurrent().getCurrentBindingsEntry();
    }

I have created a method setDeptIdInEmployee  in AMImpl and added it to client and used in the bean. Here is the code of AMImpl.

    public void setDeptIdInEmployee(Integer deptId){
        ViewObjectImpl employeesView1 = this.getEmployeesView1();
        employeesView1.setNamedWhereClauseParam("DepartmentBind", deptId);
        employeesView1.executeQuery();
    }

On running the application the following page opens

Then Click on the Show Departments button

Now click on the button open Employee and the next popUp will show Employee of Selected Department. here when clicked on Sales row

I am attaching a sample application . You can download it here  :TableOnPopupApp
Like wise you can use this to perform other operations too as now we have the select row.

Bindings in ADF

Binding provides objects to link components, it is the most innovative part of ADF after Task Flows and provides direct interaction with Appication Module. We can work with bindings in ManagedBean and also in Expression Builder. Bindings are basically used for the interaction on the model and the viewController in an ADF Application.

When we drag any DataControl on page then a binding entry is made in the pageDef of the page for that particular field. Suppose we want to Use CreateInsert operation on a button clik in the page, then we have to create the binding of CreateInsert action in the pageDef on that page and then we can use this action in our ManagedBean to perform the desired operation.

Oracle ADF provides following types of bindings:

1. Action Binding
   
   Action Binding is specifically defined for a button component. Provides access to operations defined by the business object. Such as CreateInsert , Delete.
   

   //The code below gets the Bindings entry of the binding container and fetches the current bindings entry
    BindingContainer bindings = BindingContext.getCurrent().getCurrentBindingsEntry();
    //Gets the opertaion bindings for the method "CreateInsert"
    OperationBinding operationBinding = bindings.getOperationBinding("CreateInsert");
    //Then execute executes the method of the binding
    operationBinding.execute(); 
    

   Likewise you can use the above code to call bindings in ManagedBean.
2. Iterator Binding
3. When we drag tables on the page in ADF then ADF creates a IteratorBinding in the pageDef of the page. The iterator binding can be used to get the iterator of the table in the ManagedBean.
4. Given below is the code that can be used to get the IteratorBinding in the ManagedBean.
   

       BindingContext btx = BindingContext.getCurrent();
       DCBindingContainer dcbct = (DCBindingContainer)btx.getCurrentBindingsEntry();
       DCIteratorBinding binding = dcbct.findIteratorBinding("StudentIterator");
       Row currentRow = binding.getCurrentRow();

5. Here in the last line I have get the current Row from th iterator. 

   LikeWise you can use it to perform desired action. 

7. ValueBindings
   Value Bindings are created in the pageDef for all the attributes that are added on the page from the dataControl.

Java Collections , Map Interface

Map is the most important Data Structure in Java. It is used to store Key & Value pairs.

There are commonly 4 implementations of Maps :

1. HashMap ( No Ordering on Keys or Values )
2. TreeMap ( Ordered on the basis of Key )
3. HashTable ( Implemented same as HashMap, except that HashTable is Synchronised . )
4. LinkedHashMap ( It preserves the order of insertion of elements. )

1. HashMap

   HashMap is used to store Key and Value pairs in the collection. Here is a very simple example.    
   
   
   
   import java.util.HashMap;
   import java.util.Map.Entry;
   
   public class SimpleHashMapTest {
       public SimpleHashMapTest() {
           super();
       }
   
       public static void main(String[] args) {
           //Create a hash map
           HashMap<Integer, String> map = new HashMap<Integer, String>();
           //add key value pairs in the hashMap
           map.put(1, "First");
           map.put(2, "Second");
           map.put(4, "Fourth");
           map.put(3, "Third");
           map.put(5, "Fifth");
           map.put(6, "Sixth");
           map.put(7, "Seventh");
           
           System.out.println("The key value pairs in HashMap are :");
           for(Entry<Integer,String> e : map.entrySet()){
               System.out.println("Key : "+e.getKey()+"        Val : "+e.getValue());
           }
           //get(key) is used to get the value at the given key
           System.out.println("Value at key : "+3+" is :"+map.get(3));
           //These methods can be used to check if the map contains the particular key or not. 
           //They return boolean
           map.containsKey(1);
           map.containsValue("Sixth");
       }
   }
   

   
      And the output on the console is as below.
   
   
   
   
   
   

2. TreeMap

   TreeMap is sortedd on the basis of Key. i.e. if you want to make a key-value pair that need to be sorted on the basis of the key, then you gotta use TreeMap. Let us take an example and try to understand.
   I am taking a self-defined class Animal.class as key and will make a TreeMap. So to make a self-made class a key we need to define implement following interface.
   • Comparable ( This helps in Sorting the keys by comparing them. )
      
   
   

   public class Animal implements Comparable{
       String name;
       Integer size;
       public Animal(String name, Integer size) {
           this.name = name;
           this.size = size;
       }
   
       @Override
       public int compareTo(Object o) {
           return ((Animal)o).size - this.size;
       }
       
       public String toString(){
           return size+". "+name;
       }
   }
   
   public class TreeMapTest {
     
       public static void main(String[] args) {
           TreeMap<Animal,Integer> map = new TreeMap<Animal,Integer>();
           map.put(new Animal("Elefant", 10), 1);
           map.put(new Animal("Cat", 3), 2);
           map.put(new Animal("Tiger", 7), 1);
           map.put(new Animal("Lion", 8), 1);
           map.put(new Animal("Deer", 5), 1);
           
           //map.entrySet() gets you a sorted list of key - value pairs
           System.out.println("Sorted list :");
           for(Entry<Animal,Integer> e : map.entrySet()){
               System.out.println("Key is : "+e.getKey()+ " value : "+e.getValue());
           }
           
           // If you want a sorted in descending order you can use map.descendingMap()
           System.out.println("Descending order list :");
           for(Entry<Animal,Integer> e : map.descendingMap().entrySet()){
               System.out.println("Key is : "+e.getKey()+ " value : "+e.getValue());
           }
           
       }
   }
   

   
   output is  :
   

3. HashTable

   HashTable and HashMap are almost same. The little difference between them is that
   • HashTable is synchronised
   • HashMap is unsynchronised
   That means HashTable is Thread safe and HashMap is not. That simply means that if so many threads are modifying a HashTable then locking is handeled by HashTable itself whereas in case of HashMap synchronisation needs to be done.

4. LinkedHashMap

   LinkedHashMap is similar to HashMap except for the fact that LinkedHashMap maintains the insertion order of the elements in the LinkedHashMap.
   Let us take an example and try to understand.      

   public class Animal implements Comparable{
       String name;
       Integer size;
       public Animal(String name, Integer size) {
           this.name = name;
           this.size = size;
       }
   
       @Override
       public int compareTo(Object o) {
           return ((Animal)o).size - this.size;
       }
       
       public String toString(){
           return size+". "+name;
       }
   }
   
   import java.util.LinkedHashMap;
   import java.util.Map.Entry;
   import java.util.TreeMap;
   
   public class LinkedHashMapTest {
       public static void main(String[] args) {
           LinkedHashMap<Animal,Integer> map = new LinkedHashMap<Animal,Integer>();
           map.put(new Animal("Elefant", 10), 1);
           map.put(new Animal("Cat", 3), 2);
           map.put(new Animal("Tiger", 7), 1);
           map.put(new Animal("Lion", 8), 1);
           map.put(new Animal("Deer", 5), 1);
           
           //map.entrySet() gets you a list of key - value pairs
           System.out.println("List :");
           for(Entry<Animal,Integer> e : map.entrySet()){
               System.out.println("Key is : "+e.getKey()+ " value : "+e.getValue());
           }
           
          
       }
   }
   

   
   
OutPut is : 


Here you can eaisly see that the values are stored in the LinkedHashMap in the order they are inserted.