1 懶漢模式
public class Singleton {
private Singleton singleton = null;
private Singleton() {
}
public Singleton getInstance() {
if (singleton == null) {
singleton = new Singleton();
} else {
return singleton;
}
}
}
問題在於不是線程安全的。要線程安全，在getInstance前面加上synchronized關鍵字即可，但是開銷太大。
2 餓漢模式
public class Singleton {
private Singleton singleton = new Singleton();
private Singleton() {
}
public Singletion getSingleton() {
return singleton;
}
}
3 靜態內部類
public class Singleton {
private static class SingletonHolder {
private static Singleton instance = new Singleton();
}
public static Singleton getInstance() {
return SingletonHolder.instance;
}
}