public static void func1(int[] array) {
        array = new int[10];
    }

    public static void func2(int[] array) {//
        // array[0]=99;
        array = null;
    }
    public static void main2(String[] args) {
        int[] array1 = {1, 2, 3, 4};
        func1(array1);
        for (int i = 0; i < array1.length; i++) {
            System.out.print(array1[i] + " ");
        }
        System.out.println();
        int[] array2 = {1, 2, 3, 4};
        func2(array2);
        for (int i = 0; i < array2.length; i++) {
            System.out.print(array2[i] + " ");
        }
        System.out.println();
    }
}

?5.數(shù)組練習(xí)

5.1.拷貝，打印數(shù)組

Arrays.copyOf（）拷貝克隆

    public static void main(String[] args) {
        //打印數(shù)組
        int [] array ={1,2,3,4,5,6};
        int[ ]copy = Arrays.copyOf(array,array.length);//鼠標(biāo)放在copyOf點(diǎn)ctrl可以看詳細(xì)
        System.out.println( Arrays.toString(copy));
    }

5.2.拷貝輸出局部數(shù)組

copyOfRange（數(shù)組，從下標(biāo)1開始，到下標(biāo)3）；[1,3)，java一般左閉右開

    public static void main(String[] args) {
            int [] array ={1,2,3,4,5,6};
            int[] copy2=Arrays.copyOfRange(array,1,3);
            System.out.println(Arrays.toString(copy2))
            //輸出[2, 3]
        int[] copy3=Arrays.copyOfRange(array,1,13);
        System.out.println(Arrays.toString(copy3));
        //輸出[2, 3, 4, 5, 6, 0, 0, 0, 0, 0, 0, 0]
    }

5.3.拷貝

?System.arraycopy(array, 0, copy4, ?0, array.length);

       
    public static void main(String[] args) {
        int [] array ={1,2,3,4,5,6};
         // 拷貝
        int[] copy4 = new int[array.length];
        System.arraycopy(array, 0, copy4,  0, array.length);
        System.out.println(Arrays.toString(copy4));
        //[1, 2, 3, 4, 5, 6]
        //拷貝
        int[] copy5 = new int[array.length*2];
        System.arraycopy(array, 0, copy5,  0, array.length);
        System.out.println(Arrays.toString(copy5));
        //[1, 2, 3, 4, 5, 6, 0, 0, 0, 0, 0, 0]
   }

5.4.求數(shù)組中元素的平均值

avg(arr)

    public static void main(String[] args) {
        //求數(shù)組中元素的平均值
        int[] arr = {1,2,3,4,5,6};
        System.out.println(avg(arr));
    }
    public static double avg(int[] arr) {
        int sum = 0;
        for (int x : arr) {
            sum += x;
        }
        //注意這里要強(qiáng)制轉(zhuǎn)換
        return (double)sum / (double)arr.length;
    }

5.5.查找數(shù)組中指定元素(順序查找)

    public static void main(String[] args) {
        int[] arr = {1,2,3,10,5,6};
        System.out.println(find(arr, 10));
    }
    public static int find(int[] arr, int data) {
        for (int i = 0; i < arr.length; i++) {
            if (arr[i] == data) {
                return i;
            }
        }
        return -1; // 表示沒有找到
    }

5.6 數(shù)組二分查找：先排序數(shù)組，再二分查找

使array數(shù)組有序? Arrays.sort(array);

    public static void main(String[] args) {
        int[] array = {1,2,13,4,15};
        Arrays.sort(array);
        System.out.println(Arrays.toString(array));
        //輸出[1, 2, 4, 13, 15]
    }

完整代碼：

    public static void main(String[] args) {
        int[] array = {1, 2, 13, 4, 15, 12};
        Arrays.sort(array);
        System.out.println(Arrays.toString(array));
        //輸出[1, 2, 4, 13, 15]
        System.out.println(binarySearch(array, 13));//輸出4
    }

    public static int binarySearch(int[] arr, int toFind) {
        int left = 0;
        int right = arr.length - 1;
        while (left <= right) {
            int mid = (left + right) / 2;
            if (toFind < arr[mid]) {
// 去左側(cè)區(qū)間找
                right = mid - 1;
            } else if (toFind > arr[mid]) {
// 去右側(cè)區(qū)間找
                left = mid + 1;
            } else {
// 相等, 說明找到了
                return mid;
            }
        }
        // 循環(huán)結(jié)束, 說明沒找到
        return -1;
    }

5.7 數(shù)組逆序

    public static void main(String[] args) {
            int[] arr = {1, 2, 3, 4};
            reverse(arr);
            System.out.println(Arrays.toString(arr));
            //輸出[4, 3, 2, 1]
        }
        public static void reverse(int[] arr) {
            int left = 0;
            int right = arr.length - 1;
            while (left < right) {
                int tmp = arr[left];
                arr[left] = arr[right];
                arr[right] = tmp;
                left++;
                right--;
            }
        }

5.8數(shù)組元素?cái)U(kuò)大兩倍：兩種方法

public class Text02 {
    //數(shù)組元素?cái)U(kuò)大兩倍
    public static void main(String[] args) {
        int[] array = {1,2,3,4,5};
        System.out.println(Arrays.toString(array));
        //[1, 2, 3, 4, 5]
        transform(array);//它修改的是原數(shù)組的數(shù)據(jù)
        System.out. println(Arrays.toString(array)) ;
        //[2, 4, 6, 8, 10]
        int[] array1 = {1,2,3,4,5};
        System.out. println(Arrays.toString(array1)) ;
        //[1, 2, 3, 4, 5]
        int[] ret = transform2(array1);
        System.out.println(Arrays.toString(ret));
        //[2, 4, 6, 8, 10]
    }
    public static void transform(int[] array){
        for (int i = 0; i< array. length; i++) {
            array[i] = array[i]*2;
        }
    }
    public static int[] transform2(int[ ] array) {
        int[] ret = new int[array.length];
        for (int i = 0;i< array.length; i++){
            ret[i] = array[i]*2;
        }
        return ret;
    }
}

?

寫在最后：

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