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Thread: synchronized block in java

  1. #1
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    Default synchronized block in java

    Hi ! .Today i am going to ask on synchronized block.

    the general form of synchronized block is
    class table
    {
    .......

    void printTable(int n)

    {
    synchronized(object) {
    ......
    }
    }
    }

    1)Here object means object of any class.i.e we can lock object of any class besides the object of "table" class.
    2)if we place this in place of object it is possible to lock object of table class
    3)then how can we lock object of a class other than table?can you give example based on below programme?
    4) if we want to access a variable or method from table class we need object of table .
    if we lock object of table class it is not possible to an object of table class to access synchronized block of table class
    from two different places simultaneously.
    but if we lock object of another class,say X,how can the object of class X can access synchronized block of table class?
    because object of class X is not object of table.object of table only can access members of table.

    I think you got my doubt.
    I request you to clarify my doubt based on below programme.

    import java.io.*;
    class table
    {
    void printTable(int n)
    {
    synchronized(this)
    {
    for(int i=1;i<=5;i++)
    {
    System.out.println(n*i);
    try{
    Thread.sleep(500);
    }
    catch(InterruptedException ie)
    {System.out.println(ie);
    }
    }
    }
    }
    }
    class MyThread1 extends Thread
    {
    table t;
    MyThread1(table t)
    {
    this.t=t;
    }
    public void run(){
    t.printTable(5);
    }
    }
    class MyThread2 extends Thread
    {
    table t;

    MyThread2 (table t)
    {
    this.t=t;
    }
    public void run()
    {
    t.printTable(100);
    }
    }
    class synchronizedblock1
    {
    public static void main(String args[]
    )
    {
    table t=new table();
    MyThread1 t1=new MyThread1(t);
    MyThread2 t2=new MyThread2(t);
    t1.start();
    t2.start();
    }
    }
    ==========================

    output:

    5
    10
    15
    20
    25
    100
    200
    300
    400
    500


  2. #2
    Super Moderator curmudgeon's Avatar
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    Default Re: synchronized block in java

    The object you use to lock the block with isn't used to access the method, and in fact, there is nothing "magical" about it, and itcan be any object at all, a String, an array, an Object instance, anything. The object used for locking is often just a token and likely won't be accessing any of the involved code in the synchronized block.

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