单例模式的写法

/**
 * Created by yanwen.ayw on 2016/10/14.
 * desc:静态内部类实现
 */
public class Singleton {
private static Singleton ourInstance = new Singleton();

private static class InstanceHolder{
private static final Singleton INSTANCE = new Singleton();
    }

public static Singleton getInstance() {
return InstanceHolder.INSTANCE;
    }

private Singleton() {
    }

private int counter = 0;
}



/**
 * Created by yanwen.ayw on 2016/10/14.
 * desc:枚举类实现
 */
public enum EnumSingleton {
    INSTANCE;
public void doAnything(){}
}


/**
 * Created by yanwen.ayw on 2016/10/14.
 * desc:双重校验锁实现
 */
public class DoubleCheckSingleton {
private static final String TAG = "DoubleCheckSingleton";

private static volatile DoubleCheckSingleton instance ;
private DoubleCheckSingleton(){}

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


/**
 * Created by yanwen.ayw on 2016/10/14.
 * desc:恶汉式实现
 */
public class HungurySingleton {
private static final String TAG = "HungurySingleton";

private static HungurySingleton instance = new HungurySingleton();
private HungurySingleton(){}

public static HungurySingleton getInstance() {
return instance;
    }
}  


/**
 * Created by yanwen.ayw on 2016/10/14.
 * desc:懒汉式
 */
public class LazySingleton {
private static final String TAG = "LazySingleton";

private static LazySingleton instance;
private LazySingleton() {}

public static LazySingleton getInstance() {
if(instance == null){
            instance = new LazySingleton();
        }
return instance;
    }
}