Cha4-How objects behave

• a class describe what an object knows and what an object does

  • knows — instance variable
  • does — method

• parameter/argument

  • A method uses parameter.
  • A caller passes argument

  void bark(int numOfBarks){	//parameters
    ...
  }
  

  Dog d = new Dog();
  d.bark(3)	//argument
  

• Java is pass - by - value

  • pass - by - value

• method 如果设定返回值，则在方法最后必须要有返回值。但使用时不一定有变量接收

• Encapsulation

  

• default value

  • Instance variables always get a default value
  • Local variables do not get a default value. The compiler will complain if you try to use a local variable before the variable is initialized

• Comparing variables

  • ==
    • compare primitives or to see if two references refer to the same object
  • equals()
    • to see if two different objects are equal
      • such as two different String objects that both represent “hello”

• Summary

s that both represent “hello”

• Summary