JAVA学习（小白向）—成绩评比—2021-05-29

学生的成绩存放于一个矩阵，其中行表示学生，列表示科目。如：第 0 行表示第 0 个学生的数学、语文、英语成绩。要求：

1. 进行学生成绩的随机生成, 区间为 [50, 100]。
2. 找出成绩最好、最差的同学。但有挂科的同学不参加评比。

代码如下：

package a10;

import java.util.Arrays;
import java.util.Random;

/**
 * 
 * @author hengyuzuo
 *
 */
public class MissionTODO {
	/**
	 * ***********************
	 * Classification
	 * @param args Not used now.
	 * ***********************
	 */
	public static void main(String[] args) {
		// TODO Auto-generated method stub
		classification();
	}// Of main
	
	/**
	 * ************************
	 * Method unit test
	 * ************************
	 */
	public static void classification() {
		// TODO Auto-generated method stub
		int[][] tempMatrix = new int [10][3];
		Random tempRandom = new Random();
		for (int i = 0; i < tempMatrix.length; i++) {
			for (int j = 0; j < tempMatrix[0].length; j++) {
				tempMatrix[i][j] = 50 + tempRandom.nextInt(50);
			}// Of j	
		}// Of i
		
		System.out.println("Student's grades are : \r\n" + Arrays.deepToString(tempMatrix));
		
		int[] totalScore = new int [10];
		int threshold = 60;
		int max = totalScore[0];
		int min = totalScore[0];
		for (int i = 0; i < tempMatrix.length; i++) {
			for (int j = 0; j < tempMatrix[0].length; j++) {
				if (tempMatrix[i][j] < threshold) {
					totalScore[i] = 0;
					break;
				}// Of if
				
				totalScore[i] += tempMatrix[i][j];
				
			}// Of for j
			if (totalScore[i] > max) {
				max = totalScore[i];
			}// Of if
			if (totalScore[i] < min) {
				min = totalScore[i];
			}// Of if
			
		}// Of for i
		
		System.out.println("The total score of the student is : \r\n" + Arrays.toString(totalScore));
		System.out.println("The max is : \r\n" + max);
		System.out.println("The min is : \r\n" + min);
	}// Of classification
}// Of MissionTODO

运行结果：

Student's grades are : 
[[77, 78, 63], [71, 83, 63], [71, 87, 83], [82, 94, 52], [77, 72, 84], [73, 95, 76], [72, 65, 70], [94, 65, 89], [50, 88, 80], [94, 53, 55]]
The total score of the student is : 
[218, 217, 241, 0, 233, 244, 207, 248, 0, 0]
The max is : 
248
The min is : 
0

By the way:

Eclipse里//TODO 的用法是方便查找，快捷键ctrl + o

java数组的输出方式：

1. Arrays.toString 一维数组
2. Arrays.deepToString 多维数组

后来发现，在查找最小值时，并没有排除0的存在且没有学生序号，遂按照@minfanPHD的重写了
代码：

package a10;

import java.util.Arrays;
import java.util.Random;

/**
 * 
 * @author hengyuzuo
 *
 */
public class MissionTODO2 {
	/**
	 * ********************
	 * The entrance of the program.
	 * @param args
	 * ********************
	 */
	public static void main(String[] args) {
		// TODO Auto-generated method stub
		classification();
	}// Of main
	
	/**
	 * **********************
	 * Method unit test.
	 * **********************
	 */
	public static void classification() {
		//Step 1. Generate the data with n students and m courses.
		//Set these values by yourself.
		int n = 10;
		int m = 3;
		int lowerBound = 50;
		int upperBound = 100;
		int threshold = 60;
		
		//Here we have to use an object to generate random numbers.
		Random tempRandom = new Random();
		int[][] data = new int[n][m];
		for (int i = 0; i < n; i++) {
			for (int j = 0; j < m; j++) {
					data[i][j] = lowerBound +tempRandom.nextInt(upperBound-lowerBound);
				}// Of for j
		}// Of for i
		
		System.out.println("The data id : \r\n" + Arrays.deepToString(data));
		
		//Step 2.Compute the total score of each student.
		int[] totalScore = new int[n];
		for (int i = 0; i < n; i++) {
			for (int j = 0; j < m; j++) {
				if (data[i][j] < threshold) {
					totalScore[i] = 0;
					break;
				}// Of if
				
				totalScore[i] += data[i][j];
			}// Of for j
		}// Of for i 
		
		System.out.println("The total score is: \r\n" + Arrays.toString(totalScore));
		
		//Step 3.Find the best and the worst student.
		//Typical initialization for index: invalid value.
		int tempBestIndex = -1;
		int tempWorstIndex = -1;
		//Typical initialization for best and worst values.
		//They must be replaced by valid values.
		int tempBestScore = 0;
		int tempWorstScore = m * upperBound + 1;
		for (int i = 0; i < n; i++) {
			//Do not consider failed students.
			if (totalScore[i] == 0) {
				continue;
			}// Of if
			
			if (tempBestScore < totalScore[i]) {
				tempBestScore = totalScore[i];
				tempBestIndex = i;
			}// Of if
			
			//Attention: This is statement cannot be combined with the last one
			//using "else if", because a student can be both the best and the worst
			//found this bug while setting upperBound = 65.
			if (tempWorstScore > totalScore[i]) {
				tempWorstScore = totalScore[i];
				tempWorstIndex = i;
			}// Of if
		}// Of for i
		
		//Step 4.Output the student number and score.
		if (tempBestIndex == -1) {
			System.out.println("Cannot find best student.All students have failed.");
		}else {
			System.out.println("The best student is No." + tempBestIndex + " with scores: "+ Arrays.toString(data[tempBestIndex]));
		}// Of if
		
		if (tempWorstIndex == -1) {
			System.out.println("Cannot find best student.All students have failed.");
		}else {
			System.out.println("The Worst student is No." + tempWorstIndex + " with scores: "+ Arrays.toString(data[tempWorstIndex]));
		}// Of if
	}// Of classification
}// Of MissionTODO2

运行结果：

The data id : 
[[56, 75, 68], [67, 81, 51], [93, 60, 60], [76, 97, 92], [70, 73, 91], [98, 63, 60], [51, 64, 83], [81, 79, 64], [82, 53, 67], [89, 85, 51]]
The total score is: 
[0, 0, 213, 265, 234, 221, 0, 224, 0, 0]
The best student is No.4 with scores: [76, 97, 92]
The Worst student is No.2 with scores: [93, 60, 60]

小结：

1. 经常在 Eclipse 中使用鼠标右键 source -> format, 自动调整程序的格式
2. 使用了 continue, 它是指继续跳过本次循环后面的代码，直接进入下一次循环. 而 break 是跳出整个循环体.
3. switch 语句里, 如果没遇到 break, 就会继续往后执行
4. 多个单词构成一个名字, 如果是变量名、方法名，则第一个单词首字母大写；如果是类名，则所有单词首字母大写
5. nextInt 是 java.util.Random 的一种函数（功能、方法），它用于产生下一个随机整数。如果你要下一个随机实数，就应该写 nextDouble().
6. break 是针对循环体，或者 switch 语句的. 这里使用 return 直接返回, 可以无视该方法内的其余任何代码. 即使在多重循环内部, return 都是直接返回，而不会一级一级地退出.
7. 在public static fianl int ()中final 表示不可更改, 也即常数. 使用常数的好处主要在于: 如果你想修改它的值，只需要在定义这里修改就行，而不用在程序的不同地方修改