五種單例實現:
(1)餓漢模式:(線程安全,調用率高,但是不能延時加載)
public class Singleton1{
private static Singleton1 singleton1 = new Singleton1();
private Singleton1() {
}
public static Singleton1 getInstance(){
return singleton1;
}
}
(2)懶漢模式:(線程安全,調用率不高,但是可以延時加載)
public class Singleton2{
private static Singleton2 singleton2;
private Singleton2(){
}
public synchronized static Singleton2 getInstance2(){
if(singleton2 == null){
singleton2 = new Singleton2();
}
return singleton2();
}
}
(3)雙重檢測鎖模式:(由於JVM底層模型問題,偶爾會出問題,不建議使用)
public class Singleton3{
private volatile static Singleton3 singleton3;
private Singleton3(){
}
public static Singleton3 getInstance3(){
if(singleton3 == null){
synchronized (Singleton3.class){
if(singleton3 == null){
singleton3 = new Singleton3();
}
}
}
return singleton3;
}
}
(4)靜態內部類模式:(線程安全,調用率高,可以延時加載)
- 通過內部類機制使得單例對象可以延遲加載,同時內部類相當於是外部類的靜態部分,所以可以通過JVM來保證線程安全。
public class Singleton4{
private static class Singleton4Holder{
private static Singleton4 singleton4 = new Singleton4();
}
private Singleton4(){
}
public static Singleton4 getInstance(){
return Singleton4Holder.singleton4;
}
}
(5)枚舉模式:(線程安全,調用率高,不能延時加載,但是可以天然防止反射和反序列化調用)
public enum Singleton5{
singleton5
}
}