懶漢式

public class LazySingleton {
    private static LazySingleton singleton;
    private LazySingleton() {}
    public synchronized LazySingleton getInstance() {
        if (singleton == null) {
            singleton = new LazySingleton();
        }
        return singleton;
    }

}

餓漢式

public class HungarySingleton {
    private static HungarySingleton singleton = new HungarySingleton();

    private HungarySingleton(){}

    public static HungarySingleton getInstance(){
        return singleton;
    }
}
 

雙重檢查鎖

public class DoubleCheckSingleton {

    private static volatile DoubleCheckSingleton singleton;

    private DoubleCheckSingleton() {}

    public static DoubleCheckSingleton getSingleton() {
        if (singleton != null) {
            return singleton;
        } else {
            synchronized (DoubleCheckSingleton.class) {
                if (singleton == null) {
                    singleton = new DoubleCheckSingleton();
                }
                return singleton;
            }
        }
    }
}
 

使用靜態內部類

public class StaticInnerClassSingleton {

    private StaticInnerClassSingleton(){}

    private static class StaticInnerClass{
        private static StaticInnerClassSingleton singleton = new StaticInnerClassSingleton();
    }

    public StaticInnerClassSingleton getInstance(){
        return StaticInnerClass.singleton;
    }
}
 

使用列舉

public class EnumSingleton {

    private enum  Singleton{
        INSTANCE;
        EnumSingleton enumSingleton;
        Singleton(){
            synchronized (this){
                enumSingleton = new EnumSingleton();
            }
        }
    }
    public EnumSingleton getInstance(){
        return Singleton.INSTANCE.enumSingleto