I like the consistency of your braces and indentation - well done!

The nameStack_Array should beStackArray, since asmember names arecamelCase,type names ought to bePascalCase, notUpper_Snake_Case.

You'll want to implement aconstructor so that thecapacity of the object can be parameterized, and then the calling code can look like this:

StackArray foo = new StackArray(42);foo.push(bar);

The underlyingcapacity static field would need to be changed a bit though; you'll want it to be aninstance field, so that eachobject can have its own independent value. I'd keep itfinal though, because it's not a value you want to be able to modify during the lifetime of an instance - beyond theconstructor, nothing should be allowed to modify that value.

You'll want to throw an appropriateexception inexceptional situations:

if(top >= capacity) {    System.out.println("StackOverflow !!");

AStack is adata structure; other code will rely on its correct behavior, andexpect a number of errors to occur in certain specific situations - for example when the caller attempts topush an element into an instance that already contains as many items as it can hold.

That said, I'd prefer aStack implementation that simply increases its capacity as items are pushed. In any case, printing "StackOverflow !!" isn't appropriate. Making the method return abool that the calling code can evaluate to determine whether the push/pull succeeded or not, would be a better alternative if youreally want a fixed capacity.

Printing to the console isn't the job of a data structure,printStack should be replaced by a method thatreturns a new data structure that contains acopy of the internal array. Such atoArray method would leave it up to the calling code to decide whether they want to print the items to the console, or dump them into a log file, or whatever.

Your implementation is pretty bare-bones, you'll want to look at thejava.util.Stack<E> members and possibly dig into generics. The C#System.Collections.Generics.Stack<T> class could also be an inspiration.

Thepop method would be expected toreturn the popped item. Apeek method is missing, to "peek" at the next item without popping it out of the stack.

Other observations

Betweenpush andpop, the two have anif conditional, but one is no-op in the positive branch, while the other is no-op in the negative branch (/else block). It would be better to decide whether you test for the error condition[to throw an error and fail early] or if you test for the success condition[and throw an error in theelse block] - it's usually better tofail early and reduce the indentation level:

public void foo() {    if ({error condition}) {        throw new SomeException();    }    doSomething();}

Watch the spacing on either side of comparison operators:

for(int i = top; i >=0; i--) {

Give it the same whitespace as for the= assignment operator:

for(int i = top; i >= 0; i--) {

• java
• stack