Java新手，请教如何写一个接口

public interface IntStack {
public void push(int x);
public int pop();
public void show();
}

public class MyIntStack implements IntStack {
private int[] arrStack;
public MyIntStack(int length) {
arrStack = new int[length];
for( int i=0;i arrStack[i]=-1;
}
public void push(int x) {
System.out.println(x);
}
public int pop() {
System.out.println("pop");
}
public void show(){
System.out.println("show");
}
}

.......

????

public interface IntStack {
void push(int x);
int pop();
void show();
}