MySingleton.java

public class MySingleton
{
	public static MySingleton mySingleton;
	
	public static synchronized MySingleton getInstance(String tname) {
		if(mySingleton == null) {
			System.out.println("Thread " + tname + " Singleton class is null, instantiate and return the instance");
			mySingleton = new MySingleton();
		}
		else {
			System.out.println("Thread " + tname + " Singleton class is not null, returning the instance");
		}
		return mySingleton;
	}
	
	public static MySingleton getInstance(String tname) {
		if(mySingleton == null) {
			System.out.println("Thread " + tname + " Singleton class is null, instantiate and return the instance");
			mySingleton = new MySingleton();
		}
		else {
			System.out.println("Thread " + tname + " Singleton class is not null, returning the instance");
		}
		return mySingleton;
	}
}

SingletonMultipleThreadsMain.java

public class SingletonMultipleThreadsMain
{
	public static void main(String[] args) {
		for(int n=0; n<5; n++) {
			MyThread myThread = new MyThread();
            myThread.setName(String.valueOf(n));
            myThread.start();
        }
    }
    static class MyThread extends Thread
    {
    	public MyThread() {}
        
		@Override
        public void run() {
        	System.out.println("Thread " + this.getName() + " has started ");
            MySingleton.getInstance(this.getName());
            System.out.println("Thread " + this.getName() + " endend ");
        }
    }
}