1.java

// This class defines an integer stack that can hold 10 values. 
class Stack { // last in first out
    /*
     * Now, both stck and tos are private. This means that they cannot be
     * accidentally or maliciously altered in a way that would be harmful to the
     * stack.
     */
    private int stck[] = new int[10];
    private int tos;

    // Initialize top-of-stack
    public Stack() {
        tos = -1;
    }

    // Push an item onto the stack
    public void push(int item) {
        if (tos == 9)
            System.out.println("Stack is full.");
        else
            stck[++tos] = item;
    }

    // Pop an item from the stack
    public int pop() {
        if (tos < 0) {
            System.out.println("Stack underflow.");
            return 0;
        } else
            return stck[tos--];
    }
}

class TestStack {
    public static void main(String args[]) {
        Stack mystack1 = new Stack();
        Stack mystack2 = new Stack();

        // push some numbers onto the stack
        for (int i = 0; i < 10; i++)
            mystack1.push(i);
        for (int i = 10; i < 20; i++)
            mystack2.push(i);

        // pop those numbers off the stack
        System.out.println("Stack in mystack1:");
        for (int i = 0; i < 10; i++)
            System.out.println(mystack1.pop());

        System.out.println("Stack in mystack2:");
        for (int i = 0; i < 10; i++)
            System.out.println(mystack2.pop());

        // these statements are not legal
        // mystack1.tos = -2;
        // mystack2.stck[3] = 100;
    }
}