Singleton design pattern with Java

SingletonEager.java

public class SingletonEager {

	private static final SingletonEager INSTANCE = new SingletonEager();

	private SingletonEager() {
		System.out.println("in the constructor"); // this will print first
	}

	public static SingletonEager getInstance() {
		return INSTANCE;
	}
	
	public void print() {
		System.out.println("hello from eager");
	}
	
	public static void main(String[] args) {
		System.out.println("main method start");
		
		SingletonEager.getInstance().print();;
		
		System.out.println("main end");
	}

}

SingletonHolder.java

/**
 * Bill Pugh method
 * Lazily initialized since holder is an inner class and only created when getInstance() method is called.
 *
 */
public class SingletonHolder {
	
	private SingletonHolder() {
		System.out.println("in the constructor");
	}

	private static class Holder {
		private static final SingletonHolder INSTANCE = new SingletonHolder();
	}
	
	public static SingletonHolder getInstance() {
		return Holder.INSTANCE;
	}
	
	public void print() {
		System.out.println("hello from holder");
	}
	
	public static void main(String[] args) {
		System.out.println("main method start");
		
		SingletonHolder.getInstance().print();
		
		System.out.println("main end");
	}

}

SingletonLazy.java

public class SingletonLazy {

	private static SingletonLazy instance = null;

	private SingletonLazy() {
		System.out.println("in the constructor");
	}

	public static SingletonLazy getInstance() {
		if (instance == null) {
			// synchronized block to remove overhead
			synchronized (SingletonLazy.class) {
				if (instance == null) {
					// if instance is null, initialize
					instance = new SingletonLazy();
				}

			}
		}
		return instance;
	}
	
	public void print() {
		System.out.println("hello from lazy");
	}
	
	public static void main(String[] args) {
		System.out.println("main method start");
		
		SingletonLazy.getInstance().print();
		
		System.out.println("main end");
	}

}