Java基础语法3

# 方法

基本数据类型的参数传递

        public static void add(int a, int b) {
            a += 1;
            b += 1;
        }
		
        public static void main(String[] args) {
            int a = 10;
            int b = 20;
            add(a, b);
            System.out.println(a);//10
            System.out.println(b);//20
        }

引用数据类型的参数传递

        public static void add(int[] arr) {
            arr[0] = 50;
        }

        public static void main(String[] args) {
            int[] arr = {10, 20, 30};
            add(arr);
            System.out.println(Arrays.toString(arr));//50 20 30
        }

方法重载

        public static int add(int a) {
            return a * a;
        }

        public static int add(int a, int b) {
            return a * b;
        }

        public static int add(int a, int b, int c) {
            return a * b * c;
        }

方法可变参数

        public static int add(int... arr){
            int sum = 0;
            for (int i = 0; i < arr.length; i++) {
                sum+=i;
            }
            return sum;
        }

数组

一维数组

        int[] arr = new int[3];

        arr[0] = 100;
        arr[1] = 200;
        arr[2] = 300;

        for (int i = 0; i < arr.length; i++) {
            System.out.println(arr[i]);
        }

二维数组

        int[][] arr = new int[3][];

        arr[0] = new int[]{100,200};
        arr[1] = new int[]{37,45,66};
        arr[2] = new int[]{800};

        for (int i = 0; i < arr.length; i++) {
            for (int j = 0; j < arr[i].length; j++) {
                System.out.print(arr[i][j]+" ");
            }
            System.out.println();
        }

数组常用算法

        int[] arr = {24, -7, 93, 18, 31, 6};

        //最大值
        int max = arr[0];
        for (int i = 1; i < arr.length; i++) {
            if (arr[i] > max) {
                max = arr[i];
            }
        }
        System.out.println("最大值:" + max);

        //最小值
        int min = arr[0];
        for (int i = 1; i < arr.length; i++) {
            if (arr[i] < min) {
                min = arr[i];
            }
        }
        System.out.println("最小值:" + min);

        //总和
        int sum = 0;
        for (int i = 0; i < arr.length; i++) {
            sum += arr[i];
        }
        System.out.println("总和:" + sum);

        //平均值
        int avg = sum / arr.length;
        System.out.println("平均值:" + avg);

        //数组复制
        int[] arr2 = new int[arr.length];
        for (int i = 0; i < arr.length; i++) {
            arr2[i] = arr[i];
        }
        System.out.println("arr1:" + Arrays.toString(arr));
        System.out.println("arr2:" + Arrays.toString(arr2));
        System.out.println();

        //数组反转
        for (int i = 0; i < arr.length / 2; i++) {
            int temp = arr[i];
            arr[i] = arr[arr.length -1 -i];
            arr[arr.length -1 -i] = temp;
        }
        System.out.println("arr1:" + Arrays.toString(arr));

冒泡排序

        int[] arr = {24, -7, 93, 18, 31, 6};

        for (int i = 0; i < arr.length - 1; i++) { //外层循环控制轮数
            for (int j = 0; j < arr.length - 1 - i; j++) { //内层循环控制每轮比较的次数
                if (arr[j] > arr[j + 1]) {
                    int temp = arr[j];
                    arr[j] = arr[j + 1];
                    arr[j + 1] = temp;
                }
            }
        }

        for (int i = 0; i < arr.length; i++) {
            System.out.print(arr[i] + " ");
        }

选择排序

        int[] arr = {24, -7, 93, 18, 31, 6};

        for (int i = 0; i < arr.length - 1; i++) {
            for (int j = i + 1; j < arr.length; j++) {
                if (arr[i] > arr[j]) {
                    int temp = arr[j];
                    arr[j] = arr[i];
                    arr[i] = temp;
                }
            }
        }

        for (int i = 0; i < arr.length; i++) {
            System.out.print(arr[i] + " ");
        }