002—对数组的几种基本操作

package oo2_array_code_processing;

import java.util.Arrays;

/**
 * @author ALazy_cat
 * 典型的数组代码处理：
 * 1. 找出数组中最大的元素
 * 2. 计算数组元素的平均值
 * 3. 复制数组
 * 4. 颠倒数组元素的顺序
 * 5. 矩阵相乘
 */
public class ArrayCodeProcessin {
    public static void main(String[] args) {
        int[] a = new int[8];
        for(int i=0; i<a.length; i++) {
            a[i] = (int)(Math.random() * 100);
        }
        
        int[][] b = {{1, 2, 3, 4}, {4, 5, 6, 7}, {7, 8, 9, 10}};
        int[][] c = {{1, 4}, {2, 5}, {3, 6}, {4, 7}};
        System.out.println("数组: " + Arrays.toString(a));
        System.out.println("数组中最大的数: " + getMax(a));
        System.out.println("数组中所有数的平均值: " + getAverage(a));
        System.out.println("复制数组: " + Arrays.toString(copyArray(a)));
        System.out.println("颠倒数组顺序: " + Arrays.toString(reverseArray(a)));
        System.out.println("矩阵相乘:");
        //矩阵A与矩阵B相乘的条件是：A的列数 == B的行数
        if(b[0].length == c.length) {            
            int[][] d = matrixMultiply(b, c);
            for(int i=0; i<d.length; i++) {
                for(int j=0; j<d[0].length; j++) {
                    System.out.print(d[i][j] + " ");
                }
                System.out.println();
            }
        } else {
            throw new IllegalArgumentException("这两个矩阵不能相乘...");
        }
    }
    //找出数组中最大的元素
    public static int getMax(int[] a) {
        int max = Integer.MIN_VALUE;
        for( int x : a) {
            if(x > max)
                max = x;
        }
        return max;
    }
    //计算数组元素的平均值
    public static double getAverage(int[] a) {
        int sum = 0;
        double average = 0.0;
        for(int x : a) {
            sum += x;
        }
        average = sum/a.length;
        return average;
    }
    //复制数组
    public static int[] copyArray(int[] a) {
        int[] b = new int[a.length];
        for(int i=0; i<a.length; i++) {
            b[i] = a[i];
        }
        return b;
    }
    //颠倒数组元素顺序
    public static int[] reverseArray(int[] a) {
        int mid = a.length / 2;
        int temp = 0;
        for(int i=0; i<mid; i++) {
            temp = a[i];
            a[i] = a[a.length-i-1];
            a[a.length-i-1] = temp;
        }
        return a;
    }
    //矩阵相乘
    public static int[][] matrixMultiply(int[][] a, int[][] b) {
        int[][] c = new int[a.length][b[0].length];
        for(int k=0; k<a.length; k++) {
            for(int i=0; i<b[0].length; i++) {
                for(int j=0; j<b.length; j++)
                    c[k][i] += a[k][j] * b[j][i];
            }
        }
        return c;
    }
}