class Y { private int value;

public Y(int n) { value = n; } // end int constructor

public void setValue(int z) { value = z; } // end method getValue

public int getValue() { return value; } // end method getValue

public String toString () { return "From Y: " + value; } // end toString} // end class Y

class X{ static int count = 0; private int data;

public X(int n) { data = n; } // end int constructor

public int getData() { return data; } // end getData} // end class X

public class Z extends X{ private Y a = new Y(3);

public Z(int x, int y) { super(x); a.setValue(y); } // end int, int constructor public String toString () { return "From Z: " + a.getValue(); } // end toString

public static void main(String[] args) { Z myZ = new Z (5, 7); Z myY = new Z (12, 14); System.out.println("value myZ: " + myZ); System.out.println("value myY: " + myY.a); } // end main

} // end class Z

Object X

Y

Z

mvZ

5 a

7

mvY

12 a

14

Class Hierarchy – in memory

Memory Map – instance vars

Example with Static Variable

count

X.data

Y.value

Start

class Y { private int value;

public Y(int n) { value = n; } // end int constructor

public void setValue(int z) { value = z; } // end method getValue

public int getValue() { return value; } // end method getValue

public String toString () { return "From Y: " + value; } // end toString} // end class Y

class X{ static int count = 0; private int data;

public X(int n) { data = n; } // end int constructor

public int getData() { return data; } // end getData} // end class X

public class Z extends X{ private Y a = new Y(3);

public Z(int x, int y) { super(x); a.setValue(y); } // end int, int constructor public String toString () { return "From Z: " + a.getValue(); } // end toString

public static void main(String[] args) { Z myZ = new Z (5, 7); Z myY = new Z (12, 14); System.out.println("value myZ: " + myZ); System.out.println("value myY: " + myY.a); } // end main

} // end class Z

Object X

Y

Z

Class Hierarchy – in memory

Memory Map – instance vars

Example with Static Variable - 1

count

Comments:Before the program starts, but after it’s loaded into memory, the class hierarchy is loaded and the static variables are instantiated as part of the class load.

Initial

class Y { private int value;

public Y(int n) { value = n; } // end int constructor

public void setValue(int z) { value = z; } // end method getValue

public int getValue() { return value; } // end method getValue

public String toString () { return "From Y: " + value; } // end toString} // end class Y

class X{ static int count = 0; private int data;

public X(int n) { data = n; } // end int constructor

public int getData() { return data; } // end getData} // end class X

public class Z extends X{ private Y a = new Y(3);

public Z(int x, int y) { super(x); a.setValue(y); } // end int, int constructor public String toString () { return "From Z: " + a.getValue(); } // end toString

public static void main(String[] args) { Z myZ = new Z (5, 7); Z myY = new Z (12, 14); System.out.println("value myZ: " + myZ); System.out.println("value myY: " + myY.a); } // end main

} // end class Z

Object X

Y

Z

mvZ

5 a

7

Class Hierarchy – in memory

Memory Map – instance vars

Example with Static Variable - 2

count

X.data

Y.value Comments:The line just executed accomplished the

following – all the code shown in red is involved:

Reserved memory for the mvZ handle Reserved memory for a Z instance Reserved memory for a Y instance Inited X.data to 5 in this instance Inited Y.value to 7 for this Y instance Returned handle to new Y instance,

setting value Z.a Same for Z and mvZ

One

class Y { private int value;

public Y(int n) { value = n; } // end int constructor

public void setValue(int z) { value = z; } // end method getValue

public int getValue() { return value; } // end method getValue

public String toString () { return "From Y: " + value; } // end toString} // end class Y

class X{ static int count = 0; private int data;

public X(int n) { data = n; } // end int constructor

public int getData() { return data; } // end getData} // end class X

public class Z extends X{ private Y a = new Y(3);

public Z(int x, int y) { super(x); a.setValue(y); } // end int, int constructor public String toString () { return "From Z: " + a.getValue(); } // end toString

public static void main(String[] args) { Z myZ = new Z (5, 7); Z myY = new Z (12, 14); System.out.println("value myZ: " + myZ); System.out.println("value myY: " + myY.a); } // end main

} // end class Z

Object X

Y

Z

mvZ

5 a

7

mvY

12 a

14

Class Hierarchy – in memory

Memory Map – instance vars

Example with Static Variable

count

X.data

Y.value

Comments:The line just executed accomplished the

following – all the code shown in red is involved

As before for mvY

Two

class Y { private int value;

public Y(int n) { value = n; } // end int constructor

public void setValue(int z) { value = z; } // end method getValue

public int getValue() { return value; } // end method getValue

public String toString () { return "From Y: " + value; } // end toString} // end class Y

class X{ static int count = 0; private int data;

public X(int n) { data = n; } // end int constructor

public int getData() { return data; } // end getData} // end class X

public class Z extends X{ private Y a = new Y(3);

public Z(int x, int y) { super(x); a.setValue(y); } // end int, int constructor public String toString () { return "From Z: " + a.getValue(); } // end toString

public static void main(String[] args) { Z myZ = new Z (5, 7); Z myY = new Z (12, 14); System.out.println("value myZ: " + myZ); System.out.println("value myY: " + myY.a); } // end main

} // end class Z

Object X

Y

Z

mvZ

5 a

7

mvY

12 a

14

Class Hierarchy – in memory

Memory Map – instance vars

Example with Static Variable

count

X.data

Y.value

Comments:The line just executed accomplished the

following – all the code shown in red is involved

This line of code uses toString from Z, which then calls getValue in Y

Three

class Y { private int value;

public Y(int n) { value = n; } // end int constructor

public void setValue(int z) { value = z; } // end method getValue

public int getValue() { return value; } // end method getValue

public String toString () { return "From Y: " + value; } // end toString} // end class Y

class X{ static int count = 0; private int data;

public X(int n) { data = n; } // end int constructor

public int getData() { return data; } // end getData} // end class X

public class Z extends X{ private Y a = new Y(3);

public Z(int x, int y) { super(x); a.setValue(y); } // end int, int constructor public String toString () { return "From Z: " + a.getValue(); } // end toString

public static void main(String[] args) { Z myZ = new Z (5, 7); Z myY = new Z (12, 14); System.out.println("value myZ: " + myZ); System.out.println("value myY: " + myY.a); } // end main

} // end class Z

Object X

Y

Z

mvZ

5 a

7

mvY

12 a

14

Class Hierarchy – in memory

Memory Map – instance vars

Example with Static Variable

count

X.data

Y.value

Comments:The line just executed accomplished the

following – all the code shown in red is involved

Here the call is to the toString method in Y

Four