java基础第5课

work022.java

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package test02;


import java.util.Arrays;


public class work022
{


  public static void main(String[] args)
  {
    //遍历二维数组
    int b[][] = new int[][]{{1},{2,3},{4,5,6}};
    for (int i = 0; i < b.length; i++)
    {
      for (int j = 0; j < b[i].length; j++)
      {
        System.out.print(b[i][j] + " ");
      }
      System.out.println();
    }


    int myArr[][] = {{4,3},{1,2}};
    System.out.println("数组中的元素是：");
    int k = 0;
    for (int[] x1 : myArr)
    {
      k++;
      int m = 0;
      for (int x2 : x1)
      {
        m++;
        if(k == myArr.length && m == x1.length)
        {
          System.out.print(x2);  //最后一个数字不带顿号
        }
        else 
        {
          System.out.print(x2 + "、");          
        }
      }
    }
    System.out.println();

    int myArr2[] = new int[5];
    Arrays.fill(myArr2, 88);
    for (int i = 0; i < myArr2.length; i++)
    {
      System.out.println("第" + i + "个元素是：" + myArr2[i]);
    }
    System.out.println();

    int myArr3[] = new int[10];
    Arrays.fill(myArr3, 3,8,88);  //formindex,toindex
    for (int i = 0; i < myArr3.length; i++)
    {
      System.out.println("第" + i + "个元素是：" + myArr3[i]);
    }


  }


}

work023.java

package test02;


import java.util.Arrays;


public class work023
{


  public static void main(String[] args)
  {
    //数组排序
    int arr[] = new int[]{23,42,12,8};
    Arrays.sort(arr);
    for (int i = 0; i < arr.length; i++)
    {
      System.out.print(arr[i] + " ");
    }
    System.out.println();

    String arr2[] = new String[]{"b","c","a","f","d"};
    Arrays.sort(arr2);
    for (int j = 0; j < arr2.length; j++)
    {
      System.out.print(arr2[j] + " ");
    }
    System.out.println();

    //复制数组
    int arr3[] = new int[]{23,42,12};
    int arr4[] = Arrays.copyOf(arr3, 5);
    for (int k = 0; k < arr4.length; k++)
    {
      System.out.print(arr4[k] + " "); 
    }
    System.out.println();

    int arr5[] = new int[]{23,42,12,84,10};
    int arr6[] = Arrays.copyOfRange(arr5, 1, 4);
    for (int m = 0; m < arr6.length; m++)
    {
      System.out.print(arr6[m] + " ");
    }
    System.out.println();


  }


}

work024.java

package test02;


import java.util.Arrays;


public class work024
{


  public static void main(String[] args)
  {
    int arr[] = new int[]{4,25,10};
    Arrays.sort(arr);
    int index = Arrays.binarySearch(arr,0,1,8);
    System.out.println(index);  //-2
    /*
    上面代码中变量index的值是元素8，由于在指定范围内不存在元素8，
    index的值是“-”（插入点）。如果对数组进行排序，元素8应该在元素25的
    前面，因此插入点应该是元素25的索引值2，所以index的值是-2.
    */

    int arr2[] = new int[]{4,25,10};
    Arrays.sort(arr2);
    int index2 = Arrays.binarySearch(arr2, 8);
    System.out.println(index2);

    int[] arr3 = new int[]{8,1,9,4,5};
    Arrays.sort(arr3);
    int index3 = Arrays.binarySearch(arr3, 4);
    System.out.println("4的索引值是：" + index3);

    String[] str1 = new String[]{"ab","cd","ef","gh"};
    Arrays.sort(str1);
    int index4 = Arrays.binarySearch(str1, 0,2,"cd");
    System.out.println("cd的索引值是：" + index4);


  }


}