002—对数组的几种基本操作

Posted 2020-10-18

 1 package oo2_array_code_processing;
 2 
 3 import java.util.Arrays;
 4 
 5 /**
 6  * @author ALazy_cat
 7  * 典型的数组代码处理：
 8  * 1. 找出数组中最大的元素
 9  * 2. 计算数组元素的平均值
10  * 3. 复制数组
11  * 4. 颠倒数组元素的顺序
12  * 5. 矩阵相乘
13  */
14 public class ArrayCodeProcessin {
15     public static void main(String[] args) {
16         int[] a = new int[8];
17         for(int i=0; i<a.length; i++) {
18             a[i] = (int)(Math.random() * 100);
19         }
20         
21         int[][] b = {{1, 2, 3, 4}, {4, 5, 6, 7}, {7, 8, 9, 10}};
22         int[][] c = {{1, 4}, {2, 5}, {3, 6}, {4, 7}};
23         System.out.println("数组: " + Arrays.toString(a));
24         System.out.println("数组中最大的数: " + getMax(a));
25         System.out.println("数组中所有数的平均值: " + getAverage(a));
26         System.out.println("复制数组: " + Arrays.toString(copyArray(a)));
27         System.out.println("颠倒数组顺序: " + Arrays.toString(reverseArray(a)));
28         System.out.println("矩阵相乘:");
29         //矩阵A与矩阵B相乘的条件是：A的列数 == B的行数
30         if(b[0].length == c.length) {            
31             int[][] d = matrixMultiply(b, c);
32             for(int i=0; i<d.length; i++) {
33                 for(int j=0; j<d[0].length; j++) {
34                     System.out.print(d[i][j] + " ");
35                 }
36                 System.out.println();
37             }
38         } else {
39             throw new IllegalArgumentException("这两个矩阵不能相乘...");
40         }
41     }
42     //找出数组中最大的元素
43     public static int getMax(int[] a) {
44         int max = Integer.MIN_VALUE;
45         for( int x : a) {
46             if(x > max)
47                 max = x;
48         }
49         return max;
50     }
51     //计算数组元素的平均值
52     public static double getAverage(int[] a) {
53         int sum = 0;
54         double average = 0.0;
55         for(int x : a) {
56             sum += x;
57         }
58         average = sum/a.length;
59         return average;
60     }
61     //复制数组
62     public static int[] copyArray(int[] a) {
63         int[] b = new int[a.length];
64         for(int i=0; i<a.length; i++) {
65             b[i] = a[i];
66         }
67         return b;
68     }
69     //颠倒数组元素顺序
70     public static int[] reverseArray(int[] a) {
71         int mid = a.length / 2;
72         int temp = 0;
73         for(int i=0; i<mid; i++) {
74             temp = a[i];
75             a[i] = a[a.length-i-1];
76             a[a.length-i-1] = temp;
77         }
78         return a;
79     }
80     //矩阵相乘
81     public static int[][] matrixMultiply(int[][] a, int[][] b) {
82         int[][] c = new int[a.length][b[0].length];
83         for(int k=0; k<a.length; k++) {
84             for(int i=0; i<b[0].length; i++) {
85                 for(int j=0; j<b.length; j++)
86                     c[k][i] += a[k][j] * b[j][i];
87             }
88         }
89         return c;
90     }
91 }