Array类

一：Arrays类常见方法应用举例

1：toString( ) 返回数组的字符串形式

public class Test00 {
    public static void main(String[] args) {
        Integer[] integers = {1,5,7,8};
        //遍历数组 ，返回的是字符串形式
        System.out.println(Arrays.toString(integers));
    }
}

2：sort( ) 排序（自然排序和定制排序）

<1>自然排序

public class Test00 {
    public static void main(String[] args) {
        Integer[] Arr2 = {5,9,1,4,7};
        Arrays.sort(Arr2);
        System.out.println("--------排序完成----------");
        System.out.println(Arrays.toString(Arr2));
    }
}

<2>定制排序

public class Test00 {
    public static void main(String[] args) {
        Integer[] Arr2 = {5,9,1,4,7};
        Arrays.sort(Arr2);
        Arrays.sort(Arr2, new Comparator<Integer>() {
            @Override
            public int compare(Integer o1, Integer o2) {
                return  o2 - o1;
            }
        });
        System.out.println(Arrays.toString(Arr2));
    }
}

<3>模拟排序

public class Test00 {
    public static void main(String[] args) {
        int[] Arr2 = {5,9,1,4,7};
        bubble02(Arr2, new Comparator() {
            @Override
            public int compare(Object o1, Object o2) {
                int n1 = (Integer)o1;
                int n2 = (Integer)o2;
                return n2 - n1;
            }
        });
        Systen.out.println("-------排序结果---------")
        System.out.println(Arrays.toString(Arr2));
    }
    public static void bubble02(int[] arr, Comparator c) {
        int temp = 0;
        for (int i = 0; i < arr.length - 1; i++) {
            for (int j = 0; j < arr.length - 1 - i; j++) {
                //数组排序由 c.compare(arr[j], arr[j + 1])返回的值决定
                if (c.compare(arr[j], arr[j + 1] ) > 0) {
                    temp = arr[j];
                    arr[j] = arr[j + 1];
                    arr[j + 1] = temp;
                }
            }
        }
    }
}

3：binarySearch( ) 通过二分搜索法进行查找

public class Test00 {
    public static void main(String[] args) {
        Integer[] integers = {1,5,7,8};
        //1：要求该数组是有序的. 如果该数组是无序的，不能使用 binarySearch
        //2：如果数组中不存在该元素
        //     就返回 return -(low + 1); // key not found.
        //     (它应该在的位置的负数)
        System.out.println(Arrays.binarySearch(integers,8)); //3
        System.out.println(Arrays.binarySearch(integers,9)); //-5
    }
}

4：copyOf 数组元素的复制 数组元素的复制

public class Test00 {
    public static void main(String[] args) {
        Integer[] Arr1 = {1,5,7,8};
        //1. 从 arr 数组中，拷贝 arr.length 个元素到 newArr 数组中
        //2. 如果拷贝的长度 > arr.length 就在新数组的后面 增加 null
        //3. 如果拷贝长度 < 0 就抛出异常NegativeArraySizeException
        //4. 该方法的底层使用的是 System.arraycopy()
        Integer[] Arr2 = Arrays.copyOf(Arr1,4);
        System.out.println("-----拷贝执行完毕-------");
        System.out.println(Arrays.toString(Arr2));
    }
}

5：fill( ) 数组元素的填充

public class Test00 {
    public static void main(String[] args) {
        Integer[] Arr2 = {1,5,7,8};
        ///1. 使用 99 去填充 num数组，可以理解成是替换原理的元素
        Arrays.fill(Arr2,10);
        System.out.println(Arrays.toString(Arr2));
    }
}

6：alist( ) 将一组值转换为list

public class Test00 {
    public static void main(String[] args) {
        Integer[] Arr2 = {1,5,7,8};
        //1. asList 方法，会将 (2,3,4,5,6,1)数据转成一个 List 集合
        //2. 返回的 asList 编译类型 List(接口)
        //3. asList 运行类型 java.util.Arrays#ArrayList,
        // 是Arrays 类的静态内部类
        List asList = Arrays.asList(2,3,4,5,6,1);
        System.out.println("asList=" + asList);
    }
}

二：Arrays类课堂练习

package Date0901.Test01;
import java.util.Comparator;
/**
 * 作者：sakura
 * 日期：2022年09月02日 00:53
 */
public class Test00 {
    public static void main(String[] args) {
        Book[] books = new Book[4];
        books[0] = new Book("红楼梦", 100);
        books[1] = new Book("金瓶梅新", 90);
        books[2] = new Book("青年文摘20年", 5);
        books[3] = new Book("java从入门到放弃~",300);
        Pricesort(books, new Comparator() {
            @Override
            public int compare(Object o1, Object o2) {
                int n1 =  (int)o1;
                int n2 =  (int)o2;
                return n2 -n1;
            }
        });
        Namesort(books, new Comparator() {
            @Override
            public int compare(Object o1, Object o2) {
                int n1 = (int)o1;
                int n2 = (int)o2;
                return n2 -n1;
            }
        });
        System.out.println("--------排序结果--------");
        for (int i = 0; i < books.length; i++) {
            System.out.println(books[i].toString());;
        }
    }
    public static void Pricesort(Book[] book, Comparator C) {
        Book temp ;
        for (int i = 0; i < book.length; i++) {
            for (int j = 0; j < book.length -i-1 ; j++) {
                if ( (C.compare(book[j].getPrice(),book[j+1].getPrice())) >0){
                    temp = book[j];
                    book[j] = book[j + 1];
                    book[j+1] = temp;
                }
            }
        }
    }
    public static void Namesort(Book[] books,Comparator C){
        Book temp;
        for (int i = 0; i < books.length; i++) {
            for (int j = 0; j < books.length-i-1; j++) {
                if ( (C.compare(books[j].getName().length(),books[j+1].getName().length())) >0){
                    temp = books[j];
                    books[j] = books[j + 1];
                    books[j+1] = temp;
                }
            }
        }
    }
}
class Book {
    private String name;
    private int price;
    public Book(String name, int price) {
        this.name = name;
        this.price = price;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public int getPrice() {
        return price;
    }
    public void setPrice(int price) {
        this.price = price;
    }
    @Override
    public String toString() {
        return "Book{" +
                "name='" + name + '\'' +
                ", price=" + price +
                '}';
    }
}