[Java Review] 5: this and static

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The following notes are based on video series: 手把手教你用Java基础教程 - 北京尚学堂 - 马士兵

this

Keyword this
  • In a method of a class , this refers to the object that uses the method.
  • Sometime it can be used to deal with the case that member varibales and method parameters have same names. (ref. uses the closest def.)
  • this can be view as a variable, whose value is the reference of the current object.

static

Keyword static
  • In a class, a static member variable is defined to be a shared variable for the class. When the class is first used, thestatic variable is initialized. For all the instance of the class, there is only one copy of this varible.
  • When a method is defined as static, this method, as it is called, will not parsed the ref. of the instance to the method, and hence will not able to use non-static variables.
  • We can use either instance ref. or class name (without a instance) to access static members. 
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// ex: use static var as counter

public class Cat{
    private static int sid = 0; 
    private String name;
    int id;
    Cat(String name){
        this.name = name;
        id = sid++;
    }
    public void info(){
        System.out.println
            ("My name is" + name + "No." + id);
    }
    public static void main(String arg[]){
        Cat.sid = 100;
        Cat mimi = new Cat("mimi");
        Cat pipi = new Cat("pipi");
        mimi.info();
        pipi.info();
    }
}
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