Arrays.toString

@Test
public void test_15() {
    int[] oldArr = {1, 2, 3, 4, 7, 2, 3};
    System.out.println(Arrays.toString(oldArr)); // [1, 2, 3, 4, 7, 2, 3]
}

Arrays.sort

@Test
public void test_16() {
    int[] oldArr = {1, 2, 3, 4, 7, 2, 3};
    Arrays.sort(oldArr);
    System.out.println(Arrays.toString(oldArr)); // [1, 2, 2, 3, 3, 4, 7]
}

Arrays.binarySearch

@Test
public void test_17() {
    int[] oldArr = {1, 2, 3, 4, 7, 2, 3};
    //二分查找的前提是 升序排序
    Arrays.sort(oldArr);
    System.out.println(Arrays.toString(oldArr)); // [1, 2, 2, 3, 3, 4, 7]
    // 在数组oldArr中查找7，返回7的索引（排序后的索引）
    int index = Arrays.binarySearch(oldArr, 7);
    System.out.println(index); //6
    //返回结果小于0，表示在数组中不存在。返回的负数是排序以后数组 插入点的索引的负数-1
    // [1, 2, 2, 3, 3, 4, 5(插入点), 7]  插入点的索引是 6， 6的负数-6， -6-1 = -7
    System.out.println(Arrays.binarySearch(oldArr, 5)); //-7
}

Arrays.equals

@Test
public void test_18() {
    int[] arr1 = {1, 2, 3, 4, 7, 2, 3};
    int[] arr2 = {1, 2, 3, 4, 7, 2, 3};
    System.out.println(arr1.equals(arr2)); // false  比较的是地址，继承自Object
    System.out.println(Arrays.equals(arr1, arr2)); //true
}

Arrays.fill

@Test
public void test_19() {
    int[] arr1 = new int[10];
    Arrays.fill(arr1, 2); //用2 填充数组，就算有值也会被覆盖
    System.out.println(Arrays.toString(arr1)); //[2, 2, 2, 2, 2, 2, 2, 2, 2, 2]
}

Arrays.copyOf

@Test
public void test_20() {
    int[] arr1 = {1, 2, 3, 4, 7, 2, 3};
    //从0开始复制3个元素，返回新的数组
    int[] arr2 = Arrays.copyOf(arr1,3);
    System.out.println(Arrays.toString(arr2)); //[1, 2, 3]
    //从指定开始索引到指定的结束索引的元素，返回新的数组
    int[] arr3 = Arrays.copyOfRange(arr1,1,5);
    System.out.println(Arrays.toString(arr3)); //[2, 3, 4, 7]
}