Java练习_第7天

川长思鸟来 2023-07-15 13:17 20阅读 0赞

# 冒泡排序 #

使用冒泡排序，实现如下的数组从小到大排序。  
int\[\] arr = new int\[\]\{34,5,22,-98,6,-76,0,-3\};

package com.company;
    
    
    import java.lang.reflect.Array;
    import java.util.Random;
    
    public class Test_stack {
        
        public static void BubbleSort(int []array){
        
            if (array == null || array.length < 2){
        
                return;
            }
    
            int swapFlag = 0;
            for (int i = 0; i < array.length; i++){
          // 要排序n遍。
                for (int j = 1; j < array.length - i; j ++){
          // 用于控制两两交换：每一次比较，最好i个元素就拍好顺序了
                    if (array[j - 1] > array[j]){
          // 逆序
                        int temp = array[j - 1];
                        array[j - 1] = array[j];
                        array[j] = temp;
                        swapFlag = 1;
                    }
                }
    
    
                if (swapFlag == 0){
        
                    break;
                }
                swapFlag = 0;
            }
        }
    
        public static void main(String[] args) {
        
            int[] arr = new int[]{
        34,5,22,-98,6,-76,0,-3};
            BubbleSort(arr);
    
            for (int i:arr) {
        
                System.out.print(i + "\t");
            }
        }
    }

# 反转数组 #

如何反转上面的数组。请代码实现

package com.company;
    
    
    public class Test_stack {
        
        public static void ReversalArray(int []array){
        
            if (array == null || array.length < 2){
        
                return;
            }
    
            int low = 0;
            int high = array.length - 1;
            while (low < high){
        
                int temp = array[low];
                array[low] = array[high];
                array[high] = temp;
                low ++;
                high--;
            }
    
        }
    
        public static void main(String[] args) {
        
            int[] arr = new int[]{
        34,5,22,-98,6,-76,0,-3};
            ReversalArray(arr);
    
            for (int i:arr) {
        
                System.out.print(i + "\t");
            }
        }
    }

关键字：双指针

# 复制数组 #

复制上述数组，得到一个新的数组

package com.company;
    
    
    public class Test_stack {
        
        public static int[] CopyArray(int []array){
        
            if (array == null){
        
                return null;
            }
    
            int[] brr = new int[array.length];
    
            for (int i = 0; i < array.length; i++){
        
                brr[i] = array[i];
            }
    
            return brr;
        }
    
        public static void main(String[] args) {
        
            int[] arr = new int[]{
        34,5,22,-98,6,-76,0,-3};
            int [] brr = CopyArray(arr);
    
            for (int i:brr) {
        
                System.out.print(i + "\t");
            }
        }
    }

# 线性查找元素 #

使用线性查找，从上述数组中查找22是否存在。存在，返回所在位置的索引。不存在，输出提示信息。

package com.company;
    
    
    public class Test_stack {
        
        public static int searchArray(int []array, int search){
        
            if (array == null){
        
                System.out.println("找不到");
                return -1;
            }
    
            for (int i = 0; i < array.length; i++){
        
                if (array[i] == search){
        
                    return i;
                }
            }
    
            System.out.println("找不到");
            return -1;
        }
    
        public static void main(String[] args) {
        
            int[] arr = new int[]{
        34,5,22,-98,6,-76,0,-3};
            int brr = searchArray(arr, 22);
    
            System.out.print(brr + "\t");
        }
    }

# 数组常见异常 #

NullPointerException:空指针异常

*  空指针异常

NullPointerException:空指针异常
    int[] arr = null;
    arr[0];

*  ArrayIndexOutOfBoundsException:数组角标越界异常：

int [] arr = new int[3];
            System.out.print(arr[5] + "\t");