Arrays针对数组使用提供了一些实用方法

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复制数组

参数:源数组,从源数组哪个索引开始复制的偏移量,从目标数组哪个索引开始复制的偏移量,需要复制的元素个数
  • Tips:此方法不会执行自动包装盒拆包,两个数组需明确类型
    class CopyingArrays {
      public static void main(String[] args) {
          int[] arr1 = new int[5];
          int[] arr2 = new int[8];
          Arrays.fill(arr1, 11); // 填充数组1
          Arrays.fill(arr2, 22); // 填充数组2
          System.out.println("arr1 = " + Arrays.toString(arr1));
          System.out.println("arr2 = " + Arrays.toString(arr2));
    
          System.arraycopy(arr1, 0, arr2, 0, arr1.length);
          System.out.println("arr2 = " + Arrays.toString(arr2));
          int[] arr3 = new int[3];
          System.out.println("arr3 = " + Arrays.toString(arr3));
          System.arraycopy(arr2, 0, arr3, 0, arr3.length);
          System.out.println("arr3 = " + Arrays.toString(arr3));
      }
      /**
       * arr1 = [11, 11, 11, 11, 11]
       * arr2 = [22, 22, 22, 22, 22, 22, 22, 22]
       * arr2 = [11, 11, 11, 11, 11, 22, 22, 22]
       * arr3 = [0, 0, 0]
       * arr3 = [11, 11, 11]
       */
    }
    

数组的比较

数组相等的条件是元素个数必须相等,并且对应位置的元素必须相等
class CompType implements Comparable<CompType> {
    private int title;
    private int name;

    public int getTitle() {
        return title;
    }

    public void setTitle(int title) {
        this.title = title;
    }

    public int getName() {
        return name;
    }

    public void setName(int name) {
        this.name = name;
    }

    public CompType() {
    }

    private CompType(int title, int name) {
        this.title = title;
        this.name = name;
    }

    @Override
    public String toString() {
        return "CompType{" +
                "title=" + title +
                ", name=" + name +
                '}';
    }

    @Override
    public int compareTo(CompType o) {
        return Integer.compare(o.title, title); // DESC降序
    }

    public static void main(String[] args) {
        CompType[] compTypes = {
                new CompType(2, 4),
                new CompType(1, 29),
                new CompType(4, 2),
                new CompType(48, 1)
        };
        System.out.println("Before sort:" + Arrays.toString(compTypes));
        Arrays.sort(compTypes); // 实现Comparable接口
        System.out.println("After Comparable sort:" + Arrays.toString(compTypes));

        Arrays.sort(compTypes, Comparator.comparingInt(o -> o.name)); // AES升序,name
        System.out.println("After Comparator sort:" + Arrays.toString(compTypes));

        System.out.println("binarySearch:" + Arrays.binarySearch(compTypes, new CompType(2, 4), Comparator.comparingInt(o -> o.name)));
    }

    /**
     * Before sort:[CompType{title=2, name=4}, CompType{title=1, name=29}, CompType{title=4, name=2}, CompType{title=48, name=1}]
     * After sort:[CompType{title=48, name=1}, CompType{title=4, name=2}, CompType{title=2, name=4}, CompType{title=1, name=29}]
     * After Comparator sort:[CompType{title=48, name=1}, CompType{title=4, name=2}, CompType{title=2, name=4}, CompType{title=1, name=29}]
     * binarySearch:2
     */
}

数组排序

  1. 该对象实现Comparable接口,Arrays.sort(arr1)
  2. 自定义Comparator比较器,Arrays.sort(arr1,比较器)
  3. Tip:同上

在已排序的数组中查找

  • Tip:数组已经排好序,同上
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