import java.io.*;;

public class Juzhen {

}

public static void main(String[] args) throws IOException { }

// TODO Auto-generated method stub int a[][] =new int[3][3];

System.out.println("请输入3*3矩阵:"); BufferedReader br = new BufferedReader(new String str;

for(int i=0;i<3;i++)

for(int j =0;j<3;j++){ }

str = br.readLine();

a[i][j]=Integer.parseInt(str);

InputStreamReader(System.in));

int s=a[0][0]+a[1][1]+a[2][2];

System.out.println("矩阵对角元素之和为:"+s);

(3) 输入一段字符串，统计其中有多少个单词。（单词用空格隔开） package com.zhangqian.exercise1;

import java.io.*;

public class Danci {

public static void main(String[] args) throws IOException {

// TODO Auto-generated method stub System.out.println("请输入字符串:"); String str;

BufferedReader br = new BufferedReader(new