5種單例模式
阿新 • • 發佈：2019-05-12
/**
* 懶漢單例模式
*/
public class Singleton_1 {
private static Singleton_1 uniqueSingleton;
private Singleton_1 () {}
public static Singleton_1 getInstance() {
if (null == uniqueSingleton) {
uniqueSingleton = new Singleton_1();
}
return uniqueSingleton;
}
}
/**
* 同步單例模式
*/
public class Singleton_2 {
private static Singleton_2 uniqueSingleton;
private Singleton_2() {}
public static synchronized Singleton_2 getInstance() {
if (null == uniqueSingleton) {
uniqueSingleton = new Singleton_2();
}
return uniqueSingleton;
}
}
/**
* 餓漢單利模式
*/
public class Singleton_4 {
private static Singleton_4 uniqueSingleton = new Singleton_4();
private Singleton_4() {}
public static Singleton_4 getInstance() {
return uniqueSingleton;
}
}
public enum Singleton_5 {
INSTANCE;
private SingletonBean uniqueSingleton;
private Singleton_5() {
uniqueSingleton = new SingletonBean ();
}
public SingletonBean getInstance() {
return uniqueSingleton;
}
}
public class SingletonBean {
}
/**
* 雙重檢查鎖單利模式
*/
public class Singleton_3 {
private volatile static Singleton_3 uniqueSingleton;
private Singleton_3() {}
public static Singleton_3 getInstance() {
if (null == uniqueSingleton) {
synchronized (Singleton_3.class) {
if (null == uniqueSingleton) {
uniqueSingleton = new Singleton_3();
}
}
}
return uniqueSingleton;
}
}
/**
* 測試單例模式
*/
public class SingletonTest {
public static void main(String[] args) {
// TODO Auto-generated method stub
Singleton_1 instance1_1= Singleton_1.getInstance();
Singleton_1 instance1_2= Singleton_1.getInstance();
System.out.println(instance1_1 == instance1_2);
Singleton_2 instance2_1= Singleton_2.getInstance();
Singleton_2 instance2_2= Singleton_2.getInstance();
System.out.println(instance2_1 == instance2_2);
Singleton_3 instance3_1= Singleton_3.getInstance();
Singleton_3 instance3_2= Singleton_3.getInstance();
System.out.println(instance3_1 == instance3_2);
Singleton_4 instance4_1= Singleton_4.getInstance();
Singleton_4 instance4_2= Singleton_4.getInstance();
System.out.println(instance4_1 == instance4_2);
SingletonBean instance5_1= Singleton_5.INSTANCE.getInstance();
SingletonBean instance5_2= Singleton_5.INSTANCE.getInstance();
System.out.println(instance5_1 == instance5_2);
}
}