技術標籤：設計模式設計模式單例模式

1 單例模式

JVM提供全域性唯一的物件，例項化一次，由類自身進行例項化。

2 實現方式

2.1 懶載入

package designpattern.singleton;

/**
* @description 單例：懶載入
* @author xindaqi
* @since 2021-02-10 15:24:43
*/
public class LazyLoading {

    private static LazyLoading instance;

    private LazyLoading() {}

    private static LazyLoading getInstance
 
() {
        if(instance == null) {
            instance = new LazyLoading();
        }
        return instance;
    }
    
}

2.2 預載入

package designpattern.singleton;

/**
* @description 單例模式：預載入
* @author xindaqi
* @since 2021-02-10 17:04:04
*/
public class Preloading {

    private static Preloading instance =
 
 new Preloading();

    private Preloading() {}

    private Preloading getInstance() {
        return instance;
    }
    
}

2.3 雙檢鎖

package designpattern.singleton;

/**
* @description 單例模式：雙檢鎖
* @author xindaqi
* @since 2021-02-10 17:54:03
*/
public class DoubleCheckLocking {

    private volatile static
 
 DoubleCheckLocking instance;

    private DoubleCheckLocking() {}

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

2.4 內部靜態類

package designpattern.singleton;

/**
* @description 單例模式：靜態內部類
* @author xindaqi
* @since 2021-02-10 20:02:51
*/
public class StaticInside {

    private static class StaticInsideHandler {
        private static final StaticInside INSTANCE = new StaticInside();
    }

    private StaticInside() {}

    public static final StaticInside getInstance() {
        return StaticInsideHandler.INSTANCE;
    }
    
}

2.5 列舉

package designpattern.singleton;

/**
* @description 單例模式：列舉
* @author xindaqi
* @since 2021-02-10 20:09:34
*/
public enum EnumSingleton {

    INSTANCE;

    public void singletonEnumMethod() {}
    
}

3 小結

• 單例即單個例項化物件
• 執行緒安全的情況下，JVM內只有一個例項
• 例項化由類自身完成