Stack Implementation

package stack;

import java.util.Arrays;

/**
 *
 * @author Student
 * @param <T>
 */
public class StackImpl <T>implements Stack<T>{
    
    T[] stack;
    int capacity;
    int top;
    int size;
    
     /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        // TODO code application logic here
    }

    public StackImpl(int capacity){
        stack = (T[]) new Object[capacity];
        this.capacity = capacity;
        this.top = -1;
    }
    
    @Override
    public boolean isFull(){
       return capacity == size;
    }
    
    @Override
    public boolean isEmpty(){
        return top==-1;
    }
    
    @Override
    public void push (T t){
        this.top =  top++;
        if(!isFull()){
           stack[top]=t;
        }
        else{
            this.expand();
            this.push(t);
    }
        size++;
    }
    
    @Override
    public T peek(){
        return this.stack[top];
    }
    
    @Override
    public T pop(){

        T temp = this.stack[top];
        
    if(!isEmpty()){
       stack[top]= null; 
    }
    this.top = top--;
    size = size--;
    return temp;
    }

    private void expand() {
        this.capacity = this.capacity*2;
        T[] newStack = (T[]) new Object[this.capacity];
        System.arraycopy(this.stack, 0, newStack, 0, this.stack.length);
        this.stack = newStack;
        //this.stack = Arrays.copyOf(stack, capacity);
        /*T[] newStack = (T[]) new Object[this.capacity];
        for (int i = 0; i < this.stack.length; i++) {
            newStack[i] = this.stack[i];
        }
        this.stack = newStack;*/
    }
    
    @Override
    public int search(T t){
        
        for(int i = 0; i<this.stack.length; i++){
            if(t==this.stack[i]){
                return i;
            }
        }
        return -1;
    }
       
}

Stack Interface

package stack;

/**
 *
 * @author Student
 * @param <T>
 */
public interface Stack <T> {

   T pop();
   void push(T t);
   T peek();
   int search(T t);
   boolean isEmpty();
   boolean isFull();
}