Reference variable vs. Real object

This example shows what happens for the instance method, static method, variable in the inheritance.

======================== Code ========================
public class Sub extends Super{

int x = 15;
static int y = 25;
public static void main(String args[]){

//super reference and super object
Super t = new Super();
out.println(t.x + " " + t.y);
t.methodOne();
t.methodTwo();

//super reference and sub object
Super ts = new Sub ();
out.println(ts.x + " " + ts.y);
ts.methodOne();
ts.methodTwo();

//sub reference and sub object
Sub s = new Sub();
out.println(s.x + " " + s.y);
s.methodOne();
s.methodTwo();
}
static void methodOne() {out.println("Sub methodOne()");}
void methodTwo() {
out.println("Sub methodTwo()");
methodOne();
}
}

class Super{
int x = 10;
static int y = 20;
static void methodOne() {out.println("Super methodOne()");}
void methodTwo() {
out.println("Super methodTwo()");
methodOne();
}
}
================================================

======================== Answer ========================
10 20
A methodOne()
A methodTwo()
A methodOne()
10 20
A methodOne()
B methodTwo()
B methodOne()
15 25
B methodOne()
B methodTwo()
B methodOne()
================================================

======================== Conclusion ========================
static methods and variables are based on the reference type
Real object type determines which overridden method is used at runtime
================================================

SCJP

Those are my study note of the SCJP. I used those notes to prepare the SCJP exam. Wish myself have luck for the exam.


Uploaded on authorSTREAM by maggie.zhou





Uploaded on authorSTREAM by maggie.zhou





Uploaded on authorSTREAM by maggie.zhou





Uploaded on authorSTREAM by maggie.zhou

SQA

To understand what SQA doing, I create this note. The SQA is not same as quality control, it isn't testing. It is a process control to ensure the quality of software products. Hope my slides can explain the above points with details.




Uploaded on authorSTREAM by maggie.zhou