Java的4種單例模式
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第一種：線程不安全，不正確的寫法
class Singleton{
private static Singleton instance;
private Singleton(){
}
public static Singleton getInstance(){
if(instance==null){
instance=new Singleton();
}
return instance;
}
}
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第二種：線程安全，但高並發不是很理想的寫法：
class Singleton{
private static Singleton instance;
private Singleton(){
}
public static synchronized Singleton getInstance(){
if(instance==null){
instance=new Singleton();
}
return instance;
}
}
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第三種：線程安全，性能又高，這種寫法最為常見：
class Singleton{
private static Singleton instance;
private static byte[] lock=new byte[0];
private Singleton(){
}
public static synchronized Singleton getInstance(){
if(instance==null){
synchronized(lock){
if(instance==null){
instance=new Singleton();
}
}
}
return instance;
}
}
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第四種：線程安全，性能又高，這種寫法也最為常見：
class Singleton{
private static Singleton instance;
private static ReentrantLock lock=new ReentrantLock ();
private Singleton(){
}
public static synchronized Singleton getInstance(){
if(instance==null){
lock.lock();
if(instance==null){
instance=new Singleton();
}
lock.unlock();
}
return instance;
}
}