Singleton pattern - creational design pattern

1. Hungry Chinese

　　Pros: thread safe

　　Cons: Loads instantly

2. Lazy Man

　　Advantage: lazy loading

　　Disadvantage: thread insecure (double lock mechanism can be used to ensure thread safety, but the call efficiency is low)

3. Internal type singleton mode, the first two are basically not used, because this includes the advantages of the first two

　　Advantages: 1. Thread safety, 2. Lazy loading

code show as below:

package sington;

public class InnerSing {

    private InnerSing(){
    }

    public static InnerSing getIntance(){
        return InnerClass.instance;
    }

    private static class InnerClass {
        private static InnerSing instance = new InnerSing();
    }
}

 4. Enumeration class

　　Advantages: The first three cannot avoid using reflection/serialization (that is, writing to the hard disk and then reading the hard disk to create objects) to create objects,

　　　　　　The enumeration class can; (in fact, it can be written through the constructor code: object non-null judgment + error throwing can prevent reflection creation, and rewriting the readResolve() method can prevent deserialization from constructing one more object)

　　Disadvantage: not lazy loading

code show as below:

package sington;

public enum EnumSing {

    INTANCE;

    public void function(){
        System.out.println("Specific execution method");
    }
    public static EnumSing getIntance(){
        return INTANCE;
    }
}