EXAMPLE -1
class StackDemo{
public static void
main(String args[]) {
Stack st1= new
Stack();
Stack st2 = new
Stack();
// push some
numbers onto the stack
for(int i=0;
i<10; i++) st1.push(i);
for(int i=10;
i<20; i++) st2.push(i);
// pop those
numbers off the stack
System.out.println("Stack in st1:");
for(int i=0; i<10;
i++)
System.out.println(st1.pop());
System.out.println("Stack in st2:");
for(int i=0;
i<10; i++)
System.out.println(st2.pop());
// these
statements are not legal
// st1.tos = -2;
// st2.stck[3] =
100;
}
}
OUTPUT
C:\SATYA>javac StackDemo.java
C:\SATYA>java StackDemo
C:\SATYA>
EXAMPLE -2
// Improved Stack class that uses the length array member.
class Stack {
private int stk[];
private int tos;
// allocate and
initialize stack
Stack(int size) {
stk = new
int[size];
tos = -1;
}
// Push an item onto
the stack
void push(int item)
{
if(tos==stk.length-1) // use length member
System.out.println("Stack is full.");
else
stk[++tos] =
item;
}
// Pop an item from
the stack
int pop() {
if(tos < 0) {
System.out.println("Stack underflow.");
return 0;
}
else
return
stk[tos--];
}
}
class StackDemo2 {
public static void
main(String args[]) {
Stack st1 = new
Stack(5);
Stack st2 = new Stack(8);
// push some
numbers onto the stack
for(int i=0;
i<5; i++) st1.push(i);
for(int i=0;
i<8; i++) st2.push(i);
// pop those
numbers off the stack
System.out.println("Stack in mystack1:");
for(int i=0;
i<5; i++)
System.out.println(st1.pop());
System.out.println("Stack in mystack2:");
for(int i=0;
i<8; i++)
System.out.println(st2.pop());
}
}
C:\SATYA>javac StackDemo2.java
C:\SATYA>java StackDemo2
C:\SATYA>
EXAMPLE -3
// Demonstrate static variables, methods, and blocks.
class UseStaticdemo {
static int x = 3;
static int y;
static void moth(int
z) {
System.out.println("z = " +z);
System.out.println("x = " + x);
System.out.println("y = " +y);
}
static {
System.out.println("Static
block initialized.");
y = x * 4;
}
public static void
main(String args[]) {
moth(42);
}
}
OUTPUT:
C:\SATYA>javac
UseStaticdemo1.java
C:\SATYA>java UseStaticdemo1
Z = 42
X = 3
Y = 12
EXAMPLE -4
// Using abstract methods and classes.
abstract class A {
double x;
double y;
A(double a, double b)
{
x = a;
y = b;
}
// area is now an an
abstract method
abstract double
area();
}
class B extends A {
B(double a, double
b) {
super(a, b);
}
// override area for
B
double area() {
System.out.println("Inside Area for B.");
return x * y;
}
}
class C extends A {
C(double a, double
b) {
super(a, b);
}
// override area for
right C
double area() {
System.out.println("Inside Area for Triangle.");
return (x*y)/ 2;
}
}
class AbstractAreasDemo {
public static void
main(String args[]) {
// A f = new A(10, 10); // illegal now
B r = new B(9, 5);
C t = new C(10,
8);
A x;// this is OK, no object is created
x = r;
System.out.println("Area is " + x.area());
x = t;
System.out.println("Area is " + x.area());
}
}
OUTPUT:
C:\SATYA>javac
AbstractAreasDemo.java
C:\SATYA>java
AbstractAreasDemo
Inside Area for B
Area is 45.0
Inside Area for Triangle.
Area is 40.0
EXAMPLE -5
// A Simple demonstration of abstract.
abstract class A {
abstract void
call1();
// concrete methods
are still allowed in abstract classes
void call2() {
System.out.println("This is a concrete method.");
}
}
class B extends A {
void call1() {
System.out.println("B's implementation of callme.");
}
}
class AbstractDemo {
public static void
main(String args[]) {
B b = new B();
b.call1();
b.call2();
}
}
OUTPUT:
C:\SATYA>javac
AbstractDemo.java
C:\SATYA>java
AbstractDemo
B’s implementation of callme.
This is a concrete method.
EXAMPLE -6
// Demonstrate when constructors are called.
// Create a super class.
class A {
A() {
System.out.println("Inside A's constructor.");
}
}
// Create a subclass by extending class A.
class B extends A {
B() {
System.out.println("Inside B's constructor.");
}
}
// Create another subclass by extending B.
class C extends B {
C() {
System.out.println("Inside C's constructor.");
}
}
class CallingConsDemo {
public static void
main(String args[]) {
C c = new C();
}
}
OUTPUT:
C:\SATYA>javac
CallingCons.java
C:\SATYA>java CallingCons
Inside A’s constructor.
Inside B’s constructor.
Inside C’s constructor.
EXAMPLE –7
// Method overriding. demo
class A {
int i, j;
A(int a, int b) {
i = a;
j = b;
}
// display i and j
void show() {
System.out.println("i and j: " + i + " " + j);
}
}
class B extends A {
int k;
B(int a, int b, int
c) {
super(a, b);
k = c;
}
// display k -- this
overrides show() in A
void show() {
System.out.println("k: " + k);
}
}
class OverrideDemo {
public static void
main(String args[]) {
B b = new B(1, 2,
3);
b.show(); // this
calls show() in B
}
}
OUTPUT:
C:\SATYA>javac
OverrideDemo.java
C:\SATYA>java
OverrideDemo
K=3
EXAMPLE –8
// Methods with differing type signatures are overloaded --
not overridden.
class X {
int i, j;
X(int a, int b) {
i = a;
j = b;
}
// display i and j
void show() {
System.out.println("i and j: " + i + " " + j);
}
}
// Create a subclass by extending class A.
class Y extends X {
int k;
Y(int a, int b, int
c) {
super(a, b);
k = c;
}
// overload show()
void show(String
msg) {
System.out.println(msg
+ k);
}
}
class Override1 {
public static void
main(String args[]) {
Y b = new Y(1, 2,
3);
b.show("This
is k: "); // this calls show() in Y
b.show(); // this
calls show() in X
}
}
OUTPUT:
C:\SATYA>javac
OverrideDemo1.java
C:\SATYA>java OverrideDemo1
This is k:3
i and j:1 2
EXAMPLE -9
// A simple example of inheritance.
// Create a superclass.
class A {
int i, j;
void showij() {
System.out.println("i and j: " + i + " " + j);
}
}
// Create a subclass by extending class A.
class B extends A {
int k;
void showk() {
System.out.println("k: " + k);
}
void sum() {
System.out.println("i+j+k: " + (i+j+k));
}
}
class SimpleInheritance {
public static void
main(String args[]) {
A a = new A();
B b = new B();
// The superclass
may be used by itself.
b.i = 10;
b.j = 20;
System.out.println("Contents of b: ");
b.showij();
System.out.println();
/* The subclass
has access to all public members of
its superclass.
*/
b.i = 7;
b.j = 8;
b.k = 9;
System.out.println("Contents of subOb: ");
b.showij();
b.showk();
System.out.println();
System.out.println("Sum of i, j and k in b:");
b.sum();
}
}
OUTPUT:
C:\SATYA>javac
SingleInheritance.java
C:\SATYA>java SingleInheritance
Contents of b:
i and j:10 20
Contents of subOb:
i and j:7 8
k: 9
Sum of i, j and k in b:
i+j+k:24
EXAMPLE -10
// Using super to overcome name hiding.
class A {
int i;
}
// Create a subclass by extending class A.
class B extends A {
int i; // this i
hides the i in A
B(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);
}
}
class UseSuperDemo {
public static void
main(String args[]) {
B b = new B(1, 2);
b.show();
}
}
OUTPUT:
C:\SATYA>javac
UseSuperDemo.java
C:\SATYA>java UseSuperDemo
i in superclass : 1
i in subclass : 2
EXAMPLE -11
// Demonstrate static variables, methods, and blocks.
class UseStaticDemo {
static int a = 10;
static int b;
static void meth(int
x) {
System.out.println("x = " + x);
System.out.println("a = " + a);
System.out.println("b = " + b);
}
static {
System.out.println("Static
block initialized.");
b = a * 6;
}
public static void
main(String args[]) {
meth(42);
}
}
OUTPUT:
C:\SATYA>javac
UseStaticDemo.java
C:\SATYA>java UseStaticDemo
Static block initialized.
x = 42
a = 10
b = 60
EXAMPLE -12
// Dynamic Method Dispatch
class A {
void callme() {
System.out.println("Inside A's callme method");
}
}
class B extends A {
// override callme()
void callme() {
System.out.println("Inside B's callme method");
}
}
class C extends A {
// override callme()
void callme() {
System.out.println("Inside C's callme method");
}
}
class Dispatch {
public static void
main(String args[]) {
A aa = new A(); //
object of type A
B bb= new B(); //
object of type B
C cc = new C(); //
object of type C
A rr; // obtain a
reference of type A
rr = aa; // rr
refers to an A object
rr.callme(); //
calls A's version of callme
rr = bb; // rr
refers to a B object
rr.callme(); //
calls B's version of callme
rr = cc; // rr
refers to a CC object
rr.callme(); //
calls C's version of callme
}
}
OUTPUT:
C:\SATYA>javac
Dispatch.java
C:\SATYA>java Dispatch
Inside A’s callme method
Inside B’s callme method
Inside C’s callme method
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