栈的Java实现，如何改写成长尾？

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javaimport java.util.*;

public class StackDemo { static void showPush(Stack st, int a) { st.push(new Integer(a)); System.out.println(push( + a + )); System.out.println(stack: + st); }

static void showPop(Stack st) { System.out.println(pop( + st.pop() + )); System.out.println(stack: + st); }

public static void main(String[] args) { Stack st=new Stack(); showPush(st, 10); showPush(st, 20); showPop(st); showPop(st); }}

gistfile1.txt

import java.util.*; public class StackDemo { static void showpush(Stack st, int a) { st.push(new Integer(a)); System.out.println("push(" + a + ")"); System.out.println("stack: " + st); } static void showpop(Stack st) { System.out.print("pop -> "); Integer a = (Integer) st.pop(); System.out.println(a); System.out.println("stack: " + st); } public static void main(String args[]) { Stack st = new Stack(); System.out.println("stack: " + st); showpush(st, 42); showpush(st, 66); showpush(st, 99); showpop(st); showpop(st); showpop(st); try { showpop(st); } catch (EmptyStackException e) { System.out.println("empty stack"); } } }