Java基础：常用类Compare

Compare类

Comparable接口 自然排序

1.像String、包装类等实现了Comparable接口，重写了compareTo()方法
2.String、包装类重写了compareTo()方法后，进行了从小到大的排列

@Test
public void test(){
    String[] strings = {"aa", "bb", "dd", "cc"};

    Arrays.sort(strings);
    System.out.println(Arrays.toString(strings));//[aa, bb, cc, dd]
}

非包装类的自定义类

需要重写compareTo()方法

/**
 * Created by KingsLanding on 2022/6/21 17:24
 */
public class Book implements Comparable {
    private String name;
    private int price;

    public Book() {
    }

    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 +
                '}';
    }

    
    @Override
    public int compareTo(Object o) {
        //instanceof关键字：判断左边对象是否是右边类的实例
        if(o instanceof Book){
            Book book= (Book)o;
            if (this.price > book.price) {
                return 1;
            } else if (this.price < book.price) {
                return -1;
            }else {

                return this.name.compareTo(book.name);
            }
        }
//        return 0;
        throw new RuntimeException("数据不匹配");
    }
}

/**
 * 自然排序 java.lang.Comparable
 */
@Test
public void test1(){
    Book[] books = new Book[4];
    books[0]=new Book("三体",50);
    books[1]=new Book("全频段断阻式干扰",40);
    books[2]=new Book("诗云",30);
    books[3]=new Book("aaaa",30);

    Arrays.sort(books);
    System.out.println(Arrays.toString(books));//[book{name='aaaa', price=30}, book{name='bbbb', price=30}, book{name='cccc', price=40}, book{name='dddd', price=50}]
}

Comparator 定制排序：java.util.Comparator
1.背景
- 当元素的类型没有实现java.lang.Comparable接口而又不方便修改代码
- 或者实现了，但是该接口的排序规则不适合当前的操作，就可以使用Comparator的对象来排
2.重写compare(Object o1,Object o2)方法，比较o1和o2的大小
- 如果方法返回正整数，则表示o1>o2;
- 如果返回0，表示相等
- 如果返回负整数，表示o1<o2
Comparable与Comparator使用对比
- Comparable接口方式一旦确定，就保证Comparable接口实现类的对象在任何位置都可以比较大小
- Comparator接口属于临时性的比较

    @Test
    public void test2(){
        Book[] books = new Book[4];
        books[0]=new Book("三体",50);
        books[1]=new Book("全频段断阻式干扰",40);
        books[2]=new Book("诗云",30);
        books[3]=new Book("aaaa",30);

        Arrays.sort(books, new Comparator<Book>() {
            //指明商品比较大小的方式，按照产品名称从低到高排序，再按照价格从高到低
            @Override
            public int compare(Book o1, Book o2) {
                if(o1.getName().equals(o2.getName())){
                    return -Integer.compare(o1.getPrice(),o2.getPrice());
                }else {
                    return o1.getName().compareTo(o2.getName());
                }
            }
        });
        System.out.println(Arrays.toString(books));
    }

Java基础：常用类Compare

Compare类

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