//饿汉式（静态变量）
public class SigletonType01 {

    //1.构造器私有化，外部不能new
    private SigletonType01(){

    }

    //2.本类内部创建对象实例
    private final static SigletonType01 instance = new SigletonType01();

    //3.提供一个公有的静态方法，返回实例对象
    public static SigletonType01 getInstance(){
        return instance;
    }

}

@Test
public void test01(){

    SigletonType01 sigletonType01 = SigletonType01.getInstance();
    SigletonType01 sigletonType011 = SigletonType01.getInstance();
    System.out.println(sigletonType01 == sigletonType011);
    System.out.println(sigletonType01.hashCode());
    System.out.println(sigletonType011.hashCode());
    
    /*
    结果：
        true
        1568059495
        1568059495
    */
}

//饿汉式（静态代码块）
public class SigletonType02 {

    //1.构造器私有化，外部不能new
    private SigletonType02(){

    }

    //2.静态代码块中创建实例
    private final static SigletonType02 instance;
    
    static{
        instance = new SigletonType02();
    }

    //3.提供一个公有的静态方法，返回实例对象
    public static SigletonType02 getInstance(){
        return instance;
    }

}

//懒汉式（线程不安全）
public class SigletonType03 {

    //1.构造器私有化，外部不能new
    private SigletonType03(){

    }

    //2.静态代码块中创建实例
    private static SigletonType03 instance;

    //3.提供一个公有的静态方法，返回实例对象
    public static SigletonType03 getInstance(){
        if(instance == null){
            instance = new SigletonType03();
        }
        return instance;
    }

}

//懒汉式（线程安全，同步代码）
public class SigletonType04 {

    private SigletonType04(){

    }

    private static SigletonType04 instance;

    //synchronized 同步代码，解决线程不安全问题
    public static synchronized SigletonType04 getInstance(){
        if(instance == null){
            instance = new SigletonType04();
        }
        return instance;
    }
}

public class SigletonType05 {

    private SigletonType05(){

    }

    private static SigletonType05 instance;

    //synchronized 同步代码块
    public static SigletonType05 getInstance(){
        if(instance == null){
            synchronized (SigletonType05.class){
                instance = new SigletonType05();
            }
        }
        return instance;
    }
}

public class SigletonType06 {

    private SigletonType06(){

    }

    private static volatile SigletonType06 instance;
    
    public static SigletonType06 getInstance(){
        if(instance == null){
            synchronized (SigletonType06.class){
                if(instance == null){
                    instance = new SigletonType06();
                }
            }
        }
        return instance;
    }
}

public class SigletonType07 {

    private SigletonType07(){

    }

    public static class SigletonInstance{
        private static final SigletonType07 instance = new SigletonType07();
    }

    public static SigletonType07 getInstance(){
        return SigletonInstance.instance;
    }
}

enum  SigletonType08 {

    INSTANCE;

    public void method(){
        System.out.println("method");
    }
}