Program to implement Two Stacks in an Array

class Stack
{
int items[]=new int[20];
int top1,top2;
Stack()
{
top1=-1;
top2=20;
}
void push1 (int item)
{
if (top1==top2-1)
System.out.println("Stack overflow");
else
items[++top1]=item;
}/*end push1*/
void push2 (int item)
{
if (top1==top2-1)
System.out.println("Stack overflow");
else
items[--top2]=item;
}/*end push2*/
boolean isempty()
{
if (top1==-1&&top2==20)
return true;
else
return false;
}/*end isempty*/
void pop1()
{
if (isempty()==true)
{
System.out.println("Stack underflow");
}
else
{
System.out.println("Popped element from stack1: "+items[top1--]);
//display();
}
}/*end pop*/
void pop2()
{
if (isempty())
{
System.out.println("Stack underflow");
}
else
{
System.out.println("Popped element from stack2: "+items[top2++]);
//display();
}
}/*end pop*/


void stacktop1()
{
if(isempty())
System.out.println("Stack underflow ");
else
System.out.println("Stack1-Stack top : "+(items[top1]));
}/*end stacktop*/
void stacktop2()
{
if(isempty())
System.out.println("Stack underflow ");
else
System.out.println("Stack2-Stack top : "+(items[top2]));
}/*end stacktop*/


void display()
{
int i;
System.out.println("Stack 1->");
for(i=top1;i>=0;i--)
System.out.println(items[i]);
System.out.println("Stack 2->");
for(i=top2;i<=19;i++)
System.out.println(items[i]);
}/*end display*/
}
//-------------------------------------------------------------------------------------------------------------------
class TwoStacks
{
public static void main(String args[]) throws IOException
{
Stack s=new Stack();
int i,j;
for (i=1;i<=5;i++)
s.push1(10*i);
for (i=6;i<=10;i++)
s.push2(10*i);
s.display();
s.stacktop1();
s.stacktop2();
for (i=1;i<=3;i++)
{
s.pop1();
s.pop2();
}
s.display();
}/*end main*/
}


/*
Sample Input and Output :
Stack 1->
50
40
30
20
10
Stack 2->
100
90
80
70
60
Stack1-Stack top : 50
Stack2-Stack top : 100
Popped element from stack1: 50
Popped element from stack2: 100
Popped element from stack1: 40
Popped element from stack2: 90
Popped element from stack1: 30
Popped element from stack2: 80
Stack 1->
20
10
Stack 2->
70