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Stack implementation using generics bound type.


What happens in case we want to create a generic stack which should allow us to create a stack for any kind of object. For instance, I want to create a stack which should accept only string objects. Similarly I want to create a stack which accepts only integers. How can I fulfill this requirement? We can implement this using generics bound type. Using this you can add group of objects from the same family as well. Incase if your stack wants to allow the objects extended by a super class, then you need to replace Object with your super class at line no:3 , in the below example.


package com.java2novice.ds.stack;

public class MyGenericsStack<T extends Object> {

	private int stackSize;
	private T[] stackArr;
	private int top;
	
	/**
	 * constructor to create stack with size
	 * @param size
	 */
	@SuppressWarnings("unchecked")
	public MyGenericsStack(int size) {
		this.stackSize = size;
		this.stackArr = (T[]) new Object[stackSize];
		this.top = -1;
	}

	/**
	 * This method adds new entry to the top 
	 * of the stack
	 * @param entry
	 * @throws Exception 
	 */
	public void push(T entry){
		if(this.isStackFull()){
			System.out.println(("Stack is full. Increasing the capacity."));
			this.increaseStackCapacity();
		}
		System.out.println("Adding: "+entry);
		this.stackArr[++top] = entry;
	}

	/**
	 * This method removes an entry from the 
	 * top of the stack.
	 * @return
	 * @throws Exception 
	 */
	public T pop() throws Exception {
		if(this.isStackEmpty()){
			throw new Exception("Stack is empty. Can not remove element.");
		}
		T entry = this.stackArr[top--];
		System.out.println("Removed entry: "+entry);
		return entry;
	}
	
	/**
	 * This method returns top of the stack
	 * without removing it.
	 * @return
	 */
	public T peek() {
		return stackArr[top];
	}

	private void increaseStackCapacity(){
		
		@SuppressWarnings("unchecked")
		T[] newStack = (T[]) new Object[this.stackSize*2];
		for(int i=0;i<stackSize;i++){
			newStack[i] = this.stackArr[i];
		}
		this.stackArr = newStack;
		this.stackSize = this.stackSize*2;
	}
	
	/**
	 * This method returns true if the stack is 
	 * empty
	 * @return
	 */
	public boolean isStackEmpty() {
		return (top == -1);
	}

	/**
	 * This method returns true if the stack is full
	 * @return
	 */
	public boolean isStackFull() {
		return (top == stackSize - 1);
	}
	
	public static void main(String a[]){
		MyGenericsStack<String> stringStack = new MyGenericsStack<String>(2);
		stringStack.push("java2novice");
		MyGenericsStack<Integer> integerStack = new MyGenericsStack<Integer>(2);
		integerStack.push(23);
	}
}

Output:
Adding: java2novice
Adding: 23
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List of Stack Data Structure Examples

  1. Stack introduction & implementation
  2. Java Dynamic Stack Implementation
  3. Stack implementation using generics bounded type.
  4. Reverse a word or string using Stack data structure.
  5. Write a program to find out delimiter matching using stack.
  6. Convert a decimal into a binary number using stack.
  7. Towers of Hanoi implementation using stack.
  8. Evaluation of an infix expression that is fully parenthesized using stack in java.
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Prevent a method from being overridden
By specifying final keyword to the method you can avoid overriding in a subcalss. Similarlly one can use final at class level to prevent creating subclasses.
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About Author

I'm Nataraja Gootooru, programmer by profession and passionate about technologies. All examples given here are as simple as possible to help beginners. The source code is compiled and tested in my dev environment.

If you come across any mistakes or bugs, please email me to [email protected] or you can comment on the page.

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Reference: Java™ Platform Standard Ed. 7 - API Specification | Java is registered trademark of Oracle.
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