Java, can't visualize output

Question

I am super new to programming and I'm studying for a test and don't understand the output of a piece of code. I was hoping you could help me understand why the 4 is being printed at the end?

I threw the code in the Java visualizer site and I understand everything except why the line... System.out.println(myScope.z); would print the number 4?

Any help is greatly appreciated!

public class ScopeTest {
   int z;

public static void main(String[] args){

  ScopeTest myScope = new ScopeTest();
  int z = 6;
  System.out.println(z);
  myScope.doStuff();
  System.out.println(z);
  System.out.println(myScope.z);
}

void doStuff() {
  int z = 5;
  doStuff2();
  System.out.println(z);
}

void doStuff2() {
  z=4;
}
}

Answer 1

Stepping through code one line at a time is a good exercise to figure out what it is doing. You should do this with paper and pencil as well as with a debugger. So let's step through your code one line at a time in the order of execution. After each line of code, I'll explain what it does.

ScopeTest myScope = new ScopeTest();

Create a local reference variable named myScope and initialize it to an object.

int z = 6;

Create a local int variable named z and initialize it to 6.

System.out.println(z);

Print the value of the local variable z.

myScope.doStuff();

Call doStuff() on the myScope object.

int z = 5;

Create a local variable z in doStuff() and initialize it to 5.

doStuff2();

Call doStuff2()

z=4;

Set the member field named z to the value 4. And then return control back to doStuff().

System.out.println(z);

Print out the value of the local variable z. And then return control back to main().

System.out.println(z);

Print out the value of the local variable z. (Remember we are back in main() now.

System.out.println(myScope.z);

Finally, print out the member field z. (Remember its value was set back in doStuff2(). This value is remembered because this z is a member variable.)