You can use super in a subclass to refer to its immediate superclass.
super has two general forms.
To call a constructor from its superclass:
super(parameter-list);
parameter-list is defined by the constructor in the superclass. super(parameter-list) must be the first statement executed inside a subclass' constructor.Here is a demo for how to use super to call constructor from parent class.
class Box {
private double width;
private double height;
private double depth;
Box(Box ob) { // pass object to constructor
width = ob.width;
height = ob.height;
depth = ob.depth;
}
Box(double w, double h, double d) {
width = w;
height = h;
depth = d;
}
double volume() {
return width * height * depth;
}
}
class BoxWeight extends Box {
double weight; // weight of box
BoxWeight(Box ob) { // pass object to constructor
super(ob);
}
}
public class Main {
public static void main(String args[]) {
Box mybox1 = new Box(10, 20, 15);
BoxWeight myclone = new BoxWeight(mybox1);
double vol;
vol = mybox1.volume();
System.out.println("Volume of mybox1 is " + vol);
}
}
This program generates the following output:
Volume of mybox1 is 3000.0Its general form is:
super.member
member can be either a method or an instance variable.
Let's look at the following code.
class Base {
int i;
}
class SubClass extends Base {
int i; // this i hides the i in A
SubClass(int a, int b) {
super.i = a; // i in A
i = b; // i in B
}
void show() {
System.out.println("i in superclass: " + super.i);
System.out.println("i in subclass: " + i);
}
}
public class Main {
public static void main(String args[]) {
SubClass subOb = new SubClass(1, 2);
subOb.show();
}
}
This program displays the following:
i in superclass: 1
i in subclass: 2
class Box {
private double width;
private double height;
Box(Box ob) {
width = ob.width;
height = ob.height;
}
Box(double w, double h) {
width = w;
height = h;
}
Box() {
width = -1; // use -1 to indicate
height = -1; // an uninitialized
}
Box(double len) {
width = height = len;
}
double volume() {
return width * height;
}
}
class BoxProduct extends Box {
double price; // price of box
BoxProduct(BoxProduct ob) { // pass object to constructor
super(ob);
price = ob.price;
}
BoxProduct(double w, double h, double m) {
super(w, h); // call superclass constructor
price = m;
}
BoxProduct() {
super();
price = -1;
}
BoxProduct(double len, double m) {
super(len);
price = m;
}
}
class BoxSold extends BoxProduct {
double cost;
BoxSold(BoxSold ob) {
super(ob);
cost = ob.cost;
}
BoxSold(double w, double h, double m, double c) {
super(w, h, m);
cost = c;
}
BoxSold() {
super();
cost = -1;
}
BoxSold(double len, double m, double c) {
super(len, m);
cost = c;
}
}
public class Main {
public static void main(String args[]) {
BoxSold shipment1 = new BoxSold(10, 20, 10, 3.41);
double vol = shipment1.volume();
System.out.println("Volume of shipment1 is " + vol);
System.out.println("Weight of shipment1 is " + shipment1.price);
System.out.println("Shipping cost: $" + shipment1.cost);
System.out.println();
}
}
The output of this program is shown here:
Volume of shipment1 is 200.0
Weight of shipment1 is 10.0
Shipping cost: $3.41| java2s.com | Contact Us | Privacy Policy |
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