java学习日记20230407-Arrays类

Arrays类

• Arrays里面包含了一系列静态方法，用于管理和操作数组，比如排序和搜索；
• toString返回数组的字符串形式
• sort排序（自然排序和定制排序）
• binarySearch通过二分搜索法进行查找，要求必须排好序
• copyOf数组元素的复制
• fill数组元素的填充
• equals比较两个数组元素内容是否完全一致
• asList将一组值，转化为list

• public class ArraysMethods {
      public static void main(String[] args) {
          Integer[] integers = {1,20,30};
          //toString
          System.out.println(Arrays.toString(integers));
          //sort排序
          Integer[] integers1 = {1,-1,7,0,89};
          Arrays.sort(integers1);
          //实现了Comparator接口的匿名内部类
          //体现了接口编程的概念
          //源码分析：sort-binarySort-compare（通过匿名内部类来实现排序的逻辑）,动态绑定
          Arrays.sort(integers1, new Comparator<Integer>() {
              @Override
              public int compare(Integer o1, Integer o2) {
                  return o2-o1;
              }
          });
          System.out.println(Arrays.toString(integers1));
  
          Integer[] integer3 = {-1,-2,1,0,3};
          bubble02(integer3, new Comparator() {
              @Override
              public int compare(Object o1, Object o2) {
                  return (int)o1 - (int)o2;
              }
          });
          //如果数组中不存在，则返回 -（low+1）
          System.out.println(Arrays.binarySearch(integer3,2));
          System.out.println(Arrays.toString(integer3));
  
          //copyof数组元素复制，如果长度增加，则插入null
          //如果长度小于0，则发生异常 NegativeArraySizeException
          Integer[] newInteger = Arrays.copyOf(integer3,10);
          System.out.println(Arrays.toString(newInteger));
  
          //fill数组填充
          Integer[] fillInt = new Integer[]{3,4,5};
          Arrays.fill(newInteger,2);
          System.out.println(Arrays.toString(newInteger));
  
          //equals比较数组,true/false
          Integer[] newAr01 = {1,3,2};
          Integer[] newAr02 = Arrays.copyOf(newAr01,newAr01.length);
          Arrays.sort(newAr01, new Comparator<Integer>() {
              @Override
              public int compare(Integer o1, Integer o2) {
                  return (int)o2 - (int)o1;
              }
          });
          System.out.println(Arrays.toString(newAr01));
          System.out.println(Arrays.toString(newAr02));
          System.out.println(Arrays.equals(newAr01,newAr02));
  
          //adList 数组转化为List
          List<Integer> asList = Arrays.asList(newAr01);
          System.out.println(asList);
          System.out.println(asList.getClass());
      }
      //冒泡排序
      public static void bubble01(int[] arr){
          int temp = 0;
          for (int i = 0; i < arr.length-1; i++) {
              for (int j = 0; j < arr.length-i-1; j++) {
                  if(arr[j]>arr[j+1]){
                      temp = arr[j];
                      arr[j] = arr[j+1];
                      arr[j+1] = temp;
                  }
              }
          }
      }
      //模拟匿名内部类实现排序重写
      public static void bubble02(Integer[] arr, Comparator c){
          int temp = 0;
          for (int i = 0; i < arr.length-1; i++) {
              for (int j = 0; j < arr.length-i-1; j++) {
                  if(c.compare(arr[j],arr[j+1])>0){
                      temp = arr[j];
                      arr[j] = arr[j+1];
                      arr[j+1] = temp;
                  }
              }
          }
      }
  }