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Start. 14. 7. 12. 5. a. a. Example with Static Variable. 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.

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  1. Start 14 7 12 5 a a Example with Static Variable 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 Class Hierarchy – in memory Object X count Z Y Memory Map – instance vars 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 mvZ X.data mvY Y.value

  2. Initial Example with Static Variable - 1 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 Class Hierarchy – in memory Object X count Z Y Memory Map – instance vars 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 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.

  3. One 7 5 a Example with Static Variable - 2 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 Class Hierarchy – in memory Object X count Z Y Memory Map – instance vars 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 mvZ X.data • 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 Y.value

  4. Two 14 7 12 5 a a Example with Static Variable 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 Class Hierarchy – in memory Object X count Z Y Memory Map – instance vars 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 mvZ X.data Comments: The line just executed accomplished the following – all the code shown in red is involved As before for mvY mvY Y.value

  5. Three 14 7 12 5 a a Example with Static Variable 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 constructorpublic 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 Class Hierarchy – in memory Object X count Z Y Memory Map – instance vars 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 mvZ X.data 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 mvY Y.value

  6. Four 14 7 12 5 a a Example with Static Variable 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 Class Hierarchy – in memory Object X count Z Y Memory Map – instance vars 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 getValuepublic String toString () { return "From Y: " + value; } // end toString} // end class Y mvZ X.data 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 mvY Y.value

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