singleton模式的两种方法

方法一：

import java.io.ObjectStreamException;
import java.io.Serializable;


public class E1 implements Serializable {

private E1(){
//pervent from created object by reflect 
if(INSTANCE !=null) throw new RuntimeException("duplicate instance!");
}

private final static  E1 INSTANCE =new E1();

public static E1 getInstance(){
return INSTANCE;

}
public void print(){
System.out.println("singleton test");
}

// readResovle method to preserve singleton property
private Object readResolve() throws ObjectStreamException {
  return INSTANCE;   
}


public static void main(String []args){
E1 a =E1.getInstance();
E1 b =E1.getInstance();
System.out.print(a.equals(b)?true:false);
}

}

 


方法二（推荐）：

public enum E2 {
INSTANCE;

public void print(){
System.out.println("singleton test");
}

public static void main(String []args){
E2 a=E2.INSTANCE;
E2 b=E2.INSTANCE;
System.out.print(a.equals(b)?true:false);
}
}