//左老师，您看看第4题这么做可以么？ package javaTest; import java.util.HashSet; import java.util.Set; public class MessagePrint { private Set<Integer> set; private int nextPrintId; MessagePrint() { this.set = new HashSet<Integer>(); this.nextPrintId = 1; } private void printFunc(int message) { while(set.contains(message)) { print(message++); } this.nextPrintId = message; } private void print(int message) { //输出message //System.out.print(message+" "); } public void recvPrint(int message) { set.add(message); if(message == this.nextPrintId) { printFunc(message); } } public static void main(String[] args) { MessagePrint mp=new MessagePrint(); mp.recvPrint(2); mp.recvPrint(1); mp.recvPrint(4); mp.recvPrint(5); mp.recvPrint(7); mp.recvPrint(3); mp.recvPrint(9); mp.recvPrint(8); mp.recvPrint(6); } }