何时使用 object 调用方法？

Question

I am confused on when to use an object to call a method. For instance, sometimes I have to do object.someMethod() and other times the method works when it is just called someMethod() . If anyone could clarify when I need to use an object and when I do not, that would be great!

Answer 1

When you are calling non-static class members, you always need to specify the instance. However, there is one short-cut if you are inside a member function: Instead of writing this.otherMethod() , you can omit the this. part and only write otherMethod() , as it will be implicitly assumed by the compiler. It is a common situation and readability is not hurt from omitting it:

class Foo {
  public void someMethod() {
    otherMethod(); // same as calling: this.otherMethod()
  }

  public void otherMethod() {
  }
}

MyClass object = new MyClass();
object.someMethod();

MyClass object2 = new MyClass();
someMethod(); // ERROR: from the context, it is not clear which instance is meant:
              // Do you mean object.someMethod() or object2.someMethod()?

Note that it only works for methods of the same class. If you call it from outside, it will be a compile error. In the example above, it is mandatory that you explicitly write object.someMethod() or object2.someMethod() .