在Java中获取私有类的对象

Question

I am not so proficient in java, and have a small question.

A lot of times I see the following code:

public class A
{
   private class B {

       B() {
       }

       get() {
       return this;
       }
   }

   public B getB() {
      return new B().get();
   }    
}

My question is, what is the difference if getB() just returns new B() instead of new B.get() Is it just good software engineering when you do return B().get(), or is there some deeper reasoning?

Answer 1

The return this returns current instance of B . In your case new B().get(); returns new instance of B (created right now).

So return new B().get(); and new B() do the same and equivalent.

The get() method or I would say getInstance() method we can use in Singleton pattern, like:

public class B {

 private static B instance = null; 

  public static B getInstance(){
   if(instance == null){
       instance = new B();
    }

    return instance;
  }    
} 

So no matter how many times we call getInstance() , it returns the same instance

Answer 2

基本上返回“ this”的方法是没有用的-应该调用该方法的代码已经引用了该对象

Answer 3

There's no difference. Because when you create a new B() JVM will allocate a new addres for the object (eg: 100001F), and when you call new B().get() it will return the same address (100001F). If you just return new B() , it will return the same address (100001F).

My particular opinion: return new B() is the best option, because it allocate the object and return the address, instead of allocate and later invoque get() method.