6.数组使用：反转、工具类、冒泡排序

package com.atguigu.exec;
/*
 * 在mian（）方法中声明array1和array2两个变量，他们是int型数组
 * 初始化array1为 2,3,5,7,11,13,17,19
 * 显示array1的内容
 * 赋值array2变量等于array1，修改array2中偶索引元素，使其等于索引值并打印出array1
 * array1和array2的关系
 * 修改题目 实现对array2对array1的复制
 */
public class ArrayDome3 {
 public static void main(String[] args) {
  int[] array1,array2;
  
  array1 = new int[] {2,3,5,7,11,13,17,19};
  for(int i = 0;i <array1.length;i++) {
   System.out.println(array1[i]+"\t");
  }
  //赋值array2变量等于array1 将地址值赋值  而非数组的复制
  array2 = array1;
  /*
   * 复制方法
   * array2 = new int[array.length];//新的数组则必须重新new
   * for(int i = 0; i < array.length;i++){
   *   array2[i] = array1[i];
   * }
   * 
   */
  for( int i = 0;i < array2.length;i++) {
   if(i % 2 == 0) {
    array2[i] = i;
   }
  }
  
  for(int i = 0;i <array1.length;i++) {
   System.out.println(array1[i]+"\t");
  }
  
 }
}

  反转

package com.atguigu.exec;
public class ArrayDemo4 {
 public static void main(String[] args) {
  String [] arr = new String[] {"aa","bb","cc","dd","jj"};
  
  //方法一
  for(int i = 0;i < arr.length/2;i++) {
   String temp = arr[i];
   arr[i] = arr[arr.length-i-1];
   arr[arr.length-i-1] = temp;
  }
  
  //方法二
  for(int i = 0,j = arr.length-1;i < j;i++,j--) {
   String temp = arr[i];
   arr[i] = arr[j];
   arr[j] = temp;
  }  

查找

1.线性查找

boolean isFlag = true;
  String dest = "bb";
  for(int i = 0;i < arr.length;i++) {
   //判断字符是否相等:equals
   if(dest.equals(arr[i])) {
    System.out.println("找到，位置为："+i);
    isFlag = false;
    break;
   }
  }
  
  if(isFlag) {
   System.out.println("未找到");
  }

  2.二分法查找
  //前提：所查找的数组必须有序

int[] arr1 = new int[] {1,4,6,8,43,48,99,100};
  int dest1 = 48;
  int head = 0;
  int end = arr1.length-1;
  boolean isFlag1 = true;
  
  while(head <= end) {
   int middle = (end + head)/2;
   if(dest1 == arr1[middle]) {
    System.out.println("找到，位置为"+middle);
    isFlag1 = false;
    break;
   }else if(middle < dest1) {
    head = middle + 1;
   }
   else {
    end = middle -1;
   }
  }
  if(isFlag1) {
   System.out.println("未找到");
  }  
 }
}

/*
 * java.util.Arrays:操作数组的工具类，里面定义了很多操作数组的方法
 */

package com.atguigu.java;
import java.util.Arrays;
public class ArrayTest1 {
 public static void main(String[] args) {
  
  //1.boolean equals(int[] a, int[] b) 判断两个数组是否相等
  int[] arr1 = new int[] {1,2,3,4};
  int[] arr2 = new int[] {1,3,2,4};
  boolean isEquals = Arrays.equals(arr1, arr2);
  System.out.println(isEquals);
  
  //2.String toString(int[] a):输出数组信息
  System.out.println(Arrays.toString(arr2));
  
  //3.void fill(int[] a,int val):将指定值填充到数组中
  Arrays.fill(arr1,10);
  System.out.println(Arrays.toString(arr1));
  
  //4.void sort(int[] a):对数组进行排序
  Arrays.sort(arr2);
  System.out.println(Arrays.toString(arr2));
  
  //5.int binarySearch(int[] a, int key)//二分查找
  int[] arr3 = new int[] {-98,-34,2,34,54,66,79,105,210,333};
  int index = Arrays.binarySearch(arr3, 79);
  if(index >= 0) {
   System.out.println(index);
  }else {
   System.out.println("未找到");
  }
 }
}

/*
 *数值型数组中元素、最大值、最小值、平均值、总和
 */

package com.atguigu.exec;
public class ArrayDemo2 {
 public static void main(String[] args) {
  int[] arr = new int[10];
  
  for(int i = 0;i < arr.length;i++) {
   arr[i] = (int)(Math.random()*(99-10+1)+10);
  }
  
  int maxValue = arr[0];
  for(int i = 1;i < arr.length;i++) {
   if(arr[i]>maxValue) {
    maxValue = arr[i];
   }
  }
  
  int minValue = arr[0];
  for(int i = 1;i < arr.length;i++) {
   if(arr[i] < minValue) {
    minValue = arr[i];
   }
  }
  
  int sum = 0;
  for(int i = 0;i < arr.length;i++) {
   sum += arr[i];
  }
  
  int avgValue = sum / arr.length;   
 }
 
}

排序

/*
 * 数组的冒泡排序
 */

package com.atguigu.java;
public class BubbleSort {
 public static void main(String[] args) {
   
  int[] arr = new int[] {43,32,76,-98,0,64,33,11};
  for(int i = 0; i < arr.length - 1;i++) {
   for(int j = 0; j < arr.length -1-i;j++) {
    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.println(arr[i]);
  }
  
 }
}