java中数组的应用及方法

1.数组反转

import java.util.arrays;

 public class arrayreverse {
     public static void main(string[] args){
         int[] arr ={1,2,3,4,5,6,7,8,9};
         reverse(arr);
     }
     public static void reverse(int[] arr){
         for(int i=0;i<arr.length/2;i++){
             int temp = arr[i];
             arr[i] =arr[arr.length-1-i];
             arr[arr.length-1-i]=temp;
         }
         system.out.println(arrays.tostring(arr));
     }
 }

2.求最值

class  zuizhi
  {
      public static void main(string[] args)
      {
          int[] a={2,92,34,54,28};
          minmethod(a);
          maxmethod(a);
      }
      public static void minmethod(int[] a)
      {
          int min=a[0];//不能初始化为0 数组中可能有负数
          for (int i=0;i<a.length;i++ )
          {
              if(a[i]<min)
                  min=a[i];
          }
          system.out.println("数组内最小的元素是："+min);
      }
      public static void maxmethod(int[] a)
      {
          int max=a[0];//不能初始化为0 数组中可能有负数
          for (int i=0;i<a.length;i++ )
          {
              if(a[i]>max)
                  max=a[i];
          }
          system.out.println("数组内最大的元素是："+max);
      }

  }

3.折半查找

/*
  折半查找：
  3 5 7 9 10 14
  min=0 max=length-1 mid=(max+min)/2
  */
  class binarysearch
  {
      public static void main(string[] args)
      {
          int[] a={3,5,7,9,10,14};
          int index=binarysearch_1(a,7);
          system.out.println(index);
          index=binarysearch_2(a,14);
          system.out.println(index);   
      }
      public static int binarysearch_1(int[] a,int key)
      {
          int min=0,mid,max=a.length-1;
          mid=(min+max)/2;
          while (key!=a[mid])
          {
              if(a[mid]>key)
              {
                  max=mid-1;
              }
              else  if (a[mid]<key)
              {
                  min=mid+1;
              }
              if (max<min)
                  return -1;
              mid=(min+max)/2;

          }
          return mid;
      }
      public static int binarysearch_2(int[] a,int key)
      {
          int min=0,max=a.length-1,mid;
          while (min<=max)
          {
              mid =(max+min)>>1;
              if(a[mid]>key)
              {
                  max=mid-1;
              }
              else  if (a[mid]<key)
              {
                  min=mid+1;
              }
              else
                  return mid;
          }
          return -1;
      }

  }