Example 1: Java program to implement Stack
// Stack implementation in Java
class Stack {
// store elements of stack
private int arr[];
// represent top of stack
private int top;
// total capacity of the stack
private int capacity;
// Creating a stack
Stack(int size) {
// initialize the array
// initialize the stack variables
arr = new int[size];
capacity = size;
top = -1;
}
// push elements to the top of stack
public void push(int x) {
if (isFull()) {
System.out.println("Stack OverFlow");
// terminates the program
System.exit(1);
}
// insert element on top of stack
System.out.println("Inserting " + x);
arr[++top] = x;
}
// pop elements from top of stack
public int pop() {
// if stack is empty
// no element to pop
if (isEmpty()) {
System.out.println("STACK EMPTY");
// terminates the program
System.exit(1);
}
// pop element from top of stack
return arr[top--];
}
// return size of the stack
public int getSize() {
return top + 1;
}
// check if the stack is empty
public Boolean isEmpty() {
return top == -1;
}
// check if the stack is full
public Boolean isFull() {
return top == capacity - 1;
}
// display elements of stack
public void printStack() {
for (int i = 0; i <= top; i++) {
System.out.print(arr[i] + ", ");
}
}
public static void main(String[] args) {
Stack stack = new Stack(5);
stack.push(1);
stack.push(2);
stack.push(3);
System.out.print("Stack: ");
stack.printStack();
// remove element from stack
stack.pop();
System.out.println("\nAfter popping out");
stack.printStack();
}
}
Output
Inserting 1 Inserting 2 Inserting 3 Stack: 1, 2, 3, After popping out 1, 2,
In the above example, we have implemented the stack data structure in Java.
To learn more, visit Stack Data Structure.
Example 2: Implement stack using Stack class
Java provides a built Stack class that can be used to implement a stack.
import java.util.Stack;
class Main {
public static void main(String[] args) {
// create an object of Stack class
Stack<String> animals= new Stack<>();
// push elements to top of stack
animals.push("Dog");
animals.push("Horse");
animals.push("Cat");
System.out.println("Stack: " + animals);
// pop element from top of stack
animals.pop();
System.out.println("Stack after pop: " + animals);
}
}
Output
Stack: [Dog, Horse, Cat] Stack after pop: [Dog, Horse]
In the above example, we have used the Stack class to implement the stack in Java. Here,
- animals.push() - insert elements to top of the stack
- animals.pop() - remove element from the top of the stack
Notice, we have used the angle brackets <String> while creating the stack. It represents that the stack is of the generic type.
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