單例模式常用是Double Check

public class singletonObject{
    private static singletonObject instance;
    private singletonObject(){}
    public static singletonObject getInstance(){
        if(null==instance){
            sysnchronized(singletonObject.class){
                if(null==instance){
                    instance=new
 
 singletonObject();
                }
            }
        }
        return instance;
    }
}

這個既可以實現延遲載入和效能的提高,但是會有一個危險,但例項化內容較多時,進行到一半另一個執行緒就返回了,這個時候就會造成空指標異常

優雅解決這個問題的三種方法:

使用關鍵字volatile

用來確保將變數的更新操作通知到其他執行緒,具體如下:

public class singletonObject{
    private static volatile singletonObject instance;
    private
 
 singletonObject(){}
    public static singletonObject getinstance(){
        if(null==instance){
            sysnchronized(singletonObject.class){
                if(null==sysnchronized){
                    instance=new singletonObject();
                }
            }
        }
        return instance;
    }
}
 

加一個靜態類來實現例項化

public class singletonObject{
    private singletonObject(){}
    private static class InstanceHolder{
        private final static singletonObject instance=new singletonObject();
    }
    public static singletonObject(){
        return  InstanceHolder.instance;
    }
}

列舉法
這個即保證了效能又絕對的安全 ,列舉是執行緒安全的

packagecom.dmsdbj.itoo.teachingManagement.service.impl;

importsun.swing.plaf.synth.DefaultSynthStyle;

importjava.util.stream.IntStream;

/**
*CreatedbyAdministratoron2018/4/180018.
*/
publicclassSingletonObject{
    privateSingletonObject(){}
    public enum Singletos{
        INSTANCE;
        private final SingletonObject instance;
        Singletos(){
        instance=new SingletonObject();
    }
    public SingletonObjectget Instance(){
    return instance;
}

}
public static SingletonObjectget Instance(){
    return Singletos.INSTANCE.getInstance();
}
public static void main(String[]args){
     IntStream.rangeClosed(1,100).forEach(i->newThread(String.valueOf(i)){
     @Override
     public void run(){
     System.out.print(SingletonObject.getInstance()+"\n");
}
}.start());
}
}

讓我們多學習優秀的程式碼,做一個安靜的優秀美男子