As mentioned in@rolfl's to your later question, there is limited value in this class as elements cannot be easily retrieved.

Putting aside the obvious improvements to the seemingly toy implementations, you have a mistake in describing whether the stack has 'overflow' or 'underflow': the meanings should be inversed. When you try topush(int) to a full stack, that is known as anoverflow, and you need to check whether the stack is empty whenpop()-ping instead of checking for 'overflows'.

To better indicate error conditions such as those mentioned above, you can make use ofthrowingExceptions instead of a simpleSystem.out.println(). In fact, I will suggest usingSystem.err.println() at the very least to differentiate between normal and error 'outputs'.

A Java 8 way of printing the contents of the stack is to useArrays.stream(int[]):

public void display() {    Arrays.stream(stack).forEach(System.out::println);}

This usesSystem.out.println(int) as amethod reference to print eachint value on the console.

Simply running through some test operations in themain() method is also barely enough, you should consider properunit testing techniques such as using a testing framework that canarrange-act-assert for you.

Last but not least, you should also take a look at the standard JDK classes' stack implementations for greater inspiration, such as theDeque interface.

Why not just throw exceptions instead of writing something to the console? Also make use of generics? It is highly unlikely thatStack will be used only for integers. A stack implementation using arrays is good, but most of the time people also useLinkedList to implement it, so that you do not have to resize once you exceedINITIAL_CAPACITY. It all comes down to the user's choice.

Here are two implementations which can be useful:

Array implementation of Java Stack

My own Stack Implementation in Java

• java
• array
• stack