设计一个有getMin功能的栈

package Stack;

import java.util.*;
public class getMinStack {
	private Stack <Integer> stackData;
	private Stack <Integer> stackMin;
	
	public getMinStack(){
		this.stackData = new Stack <Integer> ();
		this.stackMin = new Stack <Integer> ();
	}
	
	public void push(int num){
		if(this.stackMin.empty() || this.stackMin.peek() > num){
			this.stackMin.push(num);
	}
		this.stackData.push(num);
	}
	
	public void pop(){
		if(this.stackData.empty()){
			throw new RuntimeException("Your Stack is empty.");
		}
		int value = this.stackData.peek();
		this.stackData.pop();
		if(value == this.stackMin.peek()){
			this.stackMin.pop();
		}
	}
	
	public int getMin(){
		return this.stackMin.peek();
	}
	
	public static void main(String [] args){
		getMinStack st = new getMinStack();
		st.push(3);st.push(4);st.push(5);
		st.push(1);st.push(2);st.push(3);
		System.out.println(st.getMin());st.pop();
		System.out.println(st.getMin());st.pop();
		System.out.println(st.getMin());st.pop();
		System.out.println(st.getMin());st.pop();
		System.out.println(st.getMin());st.pop();
		System.out.println(st.getMin());st.pop();
	}
}