输入一个矩阵，求矩阵的迹

package com.demo;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.Scanner;

class Matrix {
	/**
	 * 
	 */
	private int n = 0 ;
	/*
	 * The trace of Matrix
	 */
	private long sum = 0;
	private String[] s  ;
    private Scanner[] scan;
    private long[][] a;
	public Matrix() {
     creatMatrix();
	}

	private void creatMatrix(){
		System.out.println("Please input the dimension of matrix: ");
		Scanner reader = new Scanner(System.in);
		n = reader.nextInt();
		s = new String[n];
		BufferedReader stdin = new BufferedReader(new InputStreamReader(System.in));
		for (int i = 0; i < n; i++) {
			try {
				s[i] = stdin.readLine();
			} catch (IOException e) {
				e.printStackTrace();
			}
		}
	}
	public void traceOfMatrix(){
		System.out.println("Your Matrix is: ");
		scan = new Scanner[n];
		a = new long[n][n];
		for (int i = 0; i < n; i++) {
			scan[i] = new Scanner(s[i]);
		}
		for (int m = 0; m < n; m++)
			for (int j = 0; j < n; j++)
				a[m][j] = scan[m].nextLong();
		for (int i = 0; i < n; i++) {
			for (int j = 0; j < n; j++) {
				System.out.print(a[i][j] + " ");
				if (i == j) {
					sum = sum + a[i][j];
				}
			}
			System.out.println(" ");
		}
		System.out.println("The Trace of Matrix is: " + sum);
	}

}

public class Demo {
	public static void main(String[] args) {
       Matrix matrix = new Matrix();	
       matrix.traceOfMatrix();
	}
}

输出示例：

Please input the dimension of matrix: 
3
1 2 3
4 5 6
7 8 9
Your Matrix is: 
1 2 3  
4 5 6  
7 8 9  
The Trace of Matrix is: 15

InputStreamReader 是字节流通向字符流的桥梁：它使用指定的 charset 读取字节并将其解码为字符。它使用的字符集可以由名称指定或显式给定，或者可以接受平台默认的字符集。

每次调用 InputStreamReader 中的一个 read() 方法都会导致从底层输入流读取一个或多个字节。要启用从字节到字符的有效转换，可以提前从底层流读取更多的字节，使其超过满足当前读取操作所需的字节。

为了达到最高效率，可要考虑在 BufferedReader 内包装 InputStreamReader。例如：

 BufferedReader in
   = new BufferedReader(new InputStreamReader(System.in));