How Stack works : with java

Stack එකක් කියන්නෙ මොකක්ද ?  මේ blog post එකෙන් ඒ ගැන කතා කරමු.

• What is a stack?

Allows access to only one data item; the last item inserted
If you remove this item, then you can access the next-to-last item inserted

• what happens in a stack?

In a stack all insertions and deletions are made at one end (Top).
Insertions and deletions are restricted from the Middle and at the End of a Stack

Adding an item is called  Push
Removing an item is called  Pop

Elements are removed from a Stack in the reverse order of that in which the elements
      were inserted into the Stack
The elements are inserted and removed according to the Last-In-First-Out (LIFO) principle.

• Here is the java program to learn the work of a stack

StackX.java##########################################################
//tutorials_by_sathsara
//www.sathsaratutorials.blogspot.com
//On_17th_july_2020
package stack;

public class StackX {
   
    private int maxSize ;        //set the size of the stack array
    private double[] stackArray;   
    private int top;            //top of the stack
    boolean empty;

    //constructor
    public StackX(int s) {
        maxSize = s;
        stackArray = new double[maxSize];
        top = -1;
    }

    //add items to the stack from 0th position
    public void push(double j)
    {
        if(top == maxSize -1)
            System.out.println("stack is full !");
        else
        {
            stackArray[++top] =j;
            System.out.println(" value "+ j +" enterd to the stack position " + top);
        }
           
    }

   
    //removing values from the top
    public double pop()
    {
        if(top == -1)
            return 99;
       
        else
            return stackArray[top--];
           
    }
   
    //check whether the stack is empty
    public boolean isEmpty()
    {
        if(top == -1 )
           empty = true;
       
        return   empty;

    }

    //very similar to the pop
    public double peek()
    {
        if(top == -1)
            return -99;
        else
            return stackArray[top];   
    }
}

---------------------------------------------------------------------------------------------------
StackApp.java#####################################################
//tutorials_by_sathsara
//www.sathsaratutorials.blogspot.com
//On_17th_july_2020

package stack;

public class StackApp {

    public static void main(String[] args) {
       
       
        StackX st = new StackX(5);
       
        st.push(10);    //push items to the stack
        st.push(20);
        st.push(30);
        st.push(40);
        st.push(50);
        //st.push(60);
       
       
        System.out.println();        //space line only
       
        while(!st.isEmpty())        //removing values from the stack until its empty
        {
            double val = st.pop();
            System.out.println("removing value "+ val);
           
        }
       
        while(!st.isEmpty())
        {
            double val = st.peek();
            System.out.println("removing value "+ val);
           
        }
    }

}

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