SynchronizedTest1.java

package synchronizedtest1;

import java.util.logging.Level;
import java.util.logging.Logger;

public class SynchronizedTest1 {

    public static void main(String[] args) {
        A a = new A();
        B b = new B(a);
        a.start();
        b.start();
        try {
            Thread.sleep(100);
        } catch (InterruptedException ex) {
            Logger.getLogger(SynchronizedTest1.class.getName()).log(Level.SEVERE, null, ex);
        }
        System.exit(0);
    }

}

class A extends Thread {

    private Object obj;

    public A() {
        obj = new Object();
    }

    public void printChar(char value) {
        synchronized (obj) {
            while (true)
                System.out.println(value);
        }
    }

    @Override
    public void run() {
        printChar('A');
    }
}

class B extends Thread {

    private A a;

    public B(A a) {
        this.a = a;
    }

    @Override
    public void run() {
        a.printChar('B');
    }
}

SynchronizedTest2.java

package synchronizedtest2;

import java.util.logging.Level;
import java.util.logging.Logger;

public class SynchronizedTest2 {

    public static void main(String[] args) {
        A a = new A();
        B b = new B();
        C c = new C();
        D d = new D();
        a.start();
        b.start();
        c.start();
        d.start();
        try {
            Thread.sleep(100);
        } catch (InterruptedException ex) {
            Logger.getLogger(SynchronizedTest2.class.getName()).log(Level.SEVERE, null, ex);
        }
        System.exit(0);
    }
}

class A extends Thread {

    public synchronized void printChar(char value) {
        while (true)
            System.out.println(value);
    }

    @Override
    public void run() {
        printChar('A');
    }
}

class B extends Thread {

    public static synchronized void printChar(char value) {
        while (true)
            System.out.println(value);
    }

    @Override
    public void run() {
        printChar('B');
    }
}

class C extends Thread {

    public void printChar(char value) {
        synchronized (this) {
            while (true)
                System.out.println(value);
        }
    }

    @Override
    public void run() {
        printChar('C');
    }
}

class D extends Thread {

    public static void printChar(char value) {
        synchronized (D.class) {
            while (true)
                System.out.println(value);
        }
    }

    @Override
    public void run() {
        printChar('D');
    }
}

SynchronizedTest3.java

package synchronizedtest3;

import java.util.logging.Level;
import java.util.logging.Logger;

public class SynchronizedTest3 {

    public static void main(String[] args) {
        A a = new A();
        B b = new B(a);
        C c = new C(a);
        D d = new D();
        a.start();
        b.start();
        c.start();
        d.start();
        try {
            Thread.sleep(100);
        } catch (InterruptedException ex) {
            Logger.getLogger(SynchronizedTest3.class.getName()).log(Level.SEVERE, null, ex);
        }
        System.exit(0);
    }
}

class A extends Thread {

    public synchronized void printChar(char value) {
        while (true)
            System.out.println(value);
    }

    public synchronized void printString(String value) {
        while (true)
            System.out.println(value);
    }

    @Override
    public void run() {
        printChar('A');
    }
}

class B extends Thread {

    private A a;

    public B(A a) {
        this.a = a;
    }

    @Override
    public void run() {
        a.printChar('B');
    }
}

class C extends Thread {

    private A a;

    public C(A a) {
        this.a = a;
    }

    @Override
    public void run() {
        a.printString("CCC");
    }
}

class D extends A {

    @Override
    public void run() {
        printChar('D');
    }
}