Java常用API之Arrays类解读

写在开头：本文用于作者学习Java常用API

我将官方文档中Arrays类中所有API全测了一遍并打印了结果，日拱一卒，常看常新

asList

@Test
    /*
    asList
    我的理解：将任意类型的数组转成列表
    官方：返回一个任意类型的受指定数组支持的固定大小的列表。
     */
    public void test_asList(){
        List<String> a = Arrays.asList("a","b");
        System.out.println(a);//[a, b]
 
        Arrays.asList(1,2,3).forEach(System.out::println);//1 2 3
        List<Integer> integers = Arrays.asList(1, 2, 3);
        System.out.println(integers);//[1, 2, 3]
        System.out.println(Arrays.asList(1, 2, 3));//[1, 2, 3]
 
 
        List<Tuple2> tuple2s = Arrays.asList(
                new Tuple2("dahua", 100),
                new Tuple2("xiaoyabing", 99),
                new Tuple2("sangxinran", 98),
                new Tuple2("fangmangmang", 97),
                new Tuple2("dahua", 99));
        System.out.println(tuple2s);//[(dahua,100), (xiaoyabing,99), (sangxinran,98), (fangmangmang,97), (dahua,99)]
    }

binarySearch

@Test
    public void test_binarySearch(){
        /*
        输入元素，返回下标，未找到，则返回负数。
        * */
        int[] ints = new int[5];
 
        System.out.println(Arrays.binarySearch(ints, 3));//-6
        System.out.println(Arrays.binarySearch(ints, 1));//-6
        System.out.println(Arrays.binarySearch(ints, 5));//-6
 
 
        int[] numbers = {2, 4, 6, 8, 10, 12, 14};
        System.out.println(Arrays.binarySearch(numbers, 1));//-1
        System.out.println(Arrays.binarySearch(numbers, 2));//0
        System.out.println(Arrays.binarySearch(numbers, 8));//3
 
    }

copyOf

@Test
    public void test_copyOf(){
        /*
        * 复制个新数组
        * 截取或用 0 填充（如有必要），以使副本具有指定的长度。
        * 必须指定范围
        * */
        int[] numbers = {2, 4, 6, 8, 10, 12, 14};
        int[] ints = Arrays.copyOf(numbers, 5);
        System.out.println(Arrays.toString(ints));//[2, 4, 6, 8, 10]
        System.out.println(ints);//[I@3d82c5f3
 
        int[] ints1 = Arrays.copyOf(numbers, 10);
        System.out.println(Arrays.toString(ints1));//[2, 4, 6, 8, 10, 12, 14, 0, 0, 0]
 
//        Arrays.copyOf(numbers)//报错，必须指定范围
 
    }

copyOfRange

@Test
    public void test_copyOfRange(){
        /*copyOfRange
        * 将指定数组的【指定范围】复制到一个新数组。
        * */
        int[] numbers = {2, 4, 6, 8, 10, 12, 14};
        int[] ints = Arrays.copyOfRange(numbers, 3, 10);
        System.out.println(Arrays.toString(ints));//[8, 10, 12, 14, 0, 0, 0]
 
//        int[] ints1 = Arrays.copyOfRange(numbers, 10, 20);//报错，范围不能是负数，同时数组不能越界
//        System.out.println(Arrays.toString(ints1));
    }

deepEquals

@Test
    public void test_deepEquals(){
        /*deepEquals
        * 如果两个二维(不能是一维)数组指定数组彼此是深层相等 的，则返回 true。
        * 深度相等：即比较数组中的元素是否逐个相等。*/
        int[][] numbers = {{1,2},{2, 4, 6, 8, 10, 12, 14}};
        int[][] numbers1 = {{1,2,3},{2, 4, 6, 8, 10, 12, 14}};
        System.out.println(Arrays.deepEquals(numbers,numbers1));//false
 
        int[][] numbers2 = {{1,2},{2, 4, 6, 8, 10, 12, 14}};
        System.out.println(Arrays.deepEquals(numbers,numbers2));//true
    }

deepHashCode

 @Test
    public void test_deepHashCode(){
        /*deepHashCode
        返回二维数组的哈希码。
        不能是一维数组
        * */
        int[][] numbers = {{1,2},{2, 4, 6, 8, 10, 12, 14}};
        int deepHashCode = Arrays.deepHashCode(numbers);
        System.out.println(deepHashCode);//-656811770
 
        // int[] numbers1 = {2, 4, 6, 8, 10, 12, 14};
        // System.out.println(Arrays.deepHashCode(numbers1));//报错，不能是一维数组
 
    }

deepToString

@Test
    public void test_deepToString(){
        /*deepToString
        * 将二维数组转二维列表字符串
        * 我的理解：将一个二维数组以字符串的形式返回
        * 同样参数也只能是二维数组*/
        int[][] numbers = {{1,2},{2, 4, 6, 8, 10, 12, 14}};
        String deepToString = Arrays.deepToString(numbers);
        System.out.println(deepToString);//[[1, 2], [2, 4, 6, 8, 10, 12, 14]]
    }

equals

@Test
    public void test_equals(){
        /*equals
        * 如果两个指定的 object 类型数组彼此相等，则返回 true。
        * 二维数组用equals永远为false*/
        int[][] numbers = {{1,2},{2, 4, 6, 8, 10, 12, 14}};
        int[][] numbers1 = {{1,2,3},{2, 4, 6, 8, 10, 12, 14}};
        boolean equals = Arrays.equals(numbers, numbers1);//false
        System.out.println(equals);
 
        int[][] numbers2 = {{1,2},{2, 4, 6, 8, 10, 12, 14}};
        boolean equals1 = Arrays.equals(numbers, numbers2);//false
        System.out.println(equals1);
 
 
        /*一维数组才能判等*/
        int[] ints = {2, 4, 6, 8, 10, 12, 14};
        int[] ints1 = {2, 4, 6, 8, 10, 12, 14};
        int[] ints2 = {3, 4, 6, 8, 10, 12, 14};
        System.out.println(Arrays.equals(ints, ints1));//true
        System.out.println(Arrays.equals(ints, ints2));//false
    }

fill

@Test
    public void test_fill(){
        /* 数组填充 */
        int[] ints = {2, 4, 6, 8, 10, 12, 14};
        Arrays.fill(ints,9);
        System.out.println(Arrays.toString(ints));//[9, 9, 9, 9, 9, 9, 9]
 
        int[] ints1 = {2, 4, 6, 8, 10, 12, 14};
        Arrays.fill(ints1,3,5,100); // 含左不含右
        System.out.println(Arrays.toString(ints1));//[2, 4, 6, 100, 100, 12, 14]
    }

hashCode

 @Test
    public void test_hashCode(){
        /*hashCode
        * 基于指定数组的内容返回哈希码。*/
        int[] ints = {2, 4, 6, 8, 10, 12, 14};
        int i = Arrays.hashCode(ints);
        System.out.println(i);//-656843545
 
        int[][] ints1 = {{1,2,3},{2, 4, 6, 8, 10, 12, 14}};
        int i1 = Arrays.hashCode(ints1);
        System.out.println(i1);//-1646592051
 
    }

sort

@Test
    public void test_sort(){
        /* 数组排序，默认升序
        * 也可以指定范围排序（不全排） */
        int[] ints = {1,3,7,2, 4, 6, 8, 10, 12, 14};
        Arrays.sort(ints);
        System.out.println(Arrays.toString(ints));//[1, 2, 3, 4, 6, 7, 8, 10, 12, 14]
 
        int[] ints1 = {1,3,7,2, 4, 6, 8, 10, 12, 0};
        //指定某个部分排序
        Arrays.sort(ints1,3,8);
        /*下标从0开始
        * 数组不能越界*/
        System.out.println(Arrays.toString(ints1));//[1, 3, 7, 2, 4, 6, 8, 10, 12, 0]
    }

toString

@Test
    public void test_toString(){
        /* 数组转字符串 */
        int[] ints = {1,3,7,2, 4, 6, 8, 10, 12, 14};
        System.out.println(Arrays.toString(ints));//[1, 3, 7, 2, 4, 6, 8, 10, 12, 14]
    }