effecitve java 3 singleton 1

package singleton.finalfield;

import java.lang.reflect.Constructor;
import java.lang.reflect.InvocationTargetException;

class Elvis{
    public static final Elvis INSTANCE =  new Elvis();
    private Elvis(){
        //           ，             
        if (null != INSTANCE) {
            throw  new RuntimeException("Elvis is singleton class, you can not create another one !!!!!!!!!!");
        }
    }
    public void saySth(){
        System.out.println("something");
    }
}


public class FinalFieldTest {
    public static void main(String[] args) throws IllegalAccessException, InvocationTargetException, InstantiationException {
        Class elvisClass = Elvis.class;
        Constructor>[] constructors = elvisClass.getDeclaredConstructors();
        for (Constructor> constructor : constructors) {
            constructor.setAccessible(true);
        }
        Elvis elvis = (Elvis) constructors[0].newInstance();
    }
}

package singleton.staticfactorymethod;

class Elvis{
    private static final Elvis INSTANCE = new Elvis();
    private Elvis(){}
    public static Elvis getInstance(){
        return INSTANCE;
    }
}


public class StaticFactoryMethodTest {
    public static void main(String[] args) {
        Elvis instance = Elvis.getInstance();
    }
}

package singleton.antiserialization;

import java.io.*;

class Elvis implements Serializable {
    public static final  Elvis INSTANCE =  new  Elvis();
    private Elvis(){
        if (null != INSTANCE) {
            throw  new RuntimeException("Elvis is singleton class, you can not create another one !!!!!!!!!!");
        }
    }
    public void saySth(){
        System.out.println("something");
    }
    //   readResolve  ，       ，                     
    private Object readResolve(){
        return INSTANCE;
    }
}

public class AntiSerializationTest {


    public static void main(String[] args) throws IOException, ClassNotFoundException {
        ObjectInputStream objectInputStream = new ObjectInputStream(new FileInputStream("Object.txt"));
        Elvis elvis = (Elvis) objectInputStream.readObject();
        ObjectInputStream objectInputStream2 = new ObjectInputStream(new FileInputStream("Object.txt"));
        Elvis elvis2 = (Elvis) objectInputStream2.readObject();
        System.out.println(elvis == elvis2);
    }

    public static void write(String[] args) throws IOException {
        ObjectOutputStream objectOutputStream = new ObjectOutputStream(new FileOutputStream("object.txt"));
        Elvis instance = Elvis.INSTANCE;
        objectOutputStream.writeObject(instance);
        objectOutputStream.close();
    }
}

package singleton.enummethod;

import java.io.*;
import java.lang.reflect.Constructor;
import java.lang.reflect.InvocationTargetException;

enum Elvis{
    ONE;
    public void saySth(){
        System.out.println("hello");
    }
}

public class EnumTest {

    public static void main(String[] args) throws IllegalAccessException, InvocationTargetException, InstantiationException {
        Class elvisClass = Elvis.class;
        Constructor>[] declaredConstructors = elvisClass.getDeclaredConstructors();
        for (Constructor> declaredConstructor : declaredConstructors) {
            declaredConstructor.setAccessible(true);
        }
        Object o = declaredConstructors[0].newInstance();
    }

    public static void read(String[] args) throws IOException, ClassNotFoundException {
        ObjectInputStream objectInputStream = new ObjectInputStream(new FileInputStream("Object2.txt"));
        Elvis elvis = ( Elvis) objectInputStream.readObject();
        ObjectInputStream objectInputStream2 = new ObjectInputStream(new FileInputStream("Object2.txt"));
        Elvis elvis2 = (Elvis) objectInputStream2.readObject();
        System.out.println(elvis == elvis2);
    }

    public static void write(String[] args) throws IOException {
        ObjectOutputStream objectOutputStream = new ObjectOutputStream(new FileOutputStream("object2.txt"));
        objectOutputStream.writeObject(Elvis.ONE);
        objectOutputStream.close();
    }

}