Java语法混乱，调用变量方法？

Question

I have a class Ball , within it a variable velocity which is a Vector , declared as:

private Vector velocity;

Now somewhere else in the class, there is a function called bounce , declared as:

public void bounce(float surfaceTangent) {
    velocity = velocity.bounce(surfaceTangent);
}

I don't understand what that line assigning the velocity is doing, its unfamiliar syntax to me. It looks like its calling velocity's bounce function, but velocity is a variable, not a class. It doesn't have a function at all... What exactly is this doing?

Answer 1

Velocity is an instance of class Vector (confusing name here because most people would associate that type name with java.util.Vector), which has instance methods and instance variables that belong to every instance of Vector. Bounce looks like an instance method here. In object oriented programming you usually interact with objects (instances) through their methods.

but velocity is a variable, not a class. It doesn't have a function at all...

In Java, classes do have their own class methods (and class variables), these are denoted by the method modifier of static.

Answer 2

您有一个声明为velocity的变量，您要为其分配由对Velocity实例调用的方法bounce(float)返回的值。