day09-JAVA常用类、JAVA比较器（comparable、comparator）、system类、Math类、BigInteger与BigDecimal

1.自然排序：java.lang.Comparable

是一个接口，重写compareTo方法, 还可以使用Arrays.sort 或 Collections.sort方法

class A implements Comparable{

@Override

public int compareTo(Object o ){

}

}

 Comparable 的典型实现 ： ( 默认都是从小到大排列的 )

        String ：按照字符串中字符的 Unicode 值进行比较

        Character ：按照字符的 Unicode 值来进行比较

        数值类型对应的包装类以及 BigInteger 、 BigDecimal ：按照它们对应的数值大小进行比较

        Boolean ： true 对应的包装类实例大于 false 对应的包装类实例

        Date 、 Time 等：后面的日期时间比前面的日期时间大

public class ComparableTest {
    public static void main(String[] args) {
        Goods g1 = new Goods("三国",18);
        Goods g2 = new Goods("水浒",29);

        System.out.println(g1.compareTo(g2));

        Goods [] all = new Goods[4];
        all[0]=new Goods("111",2);
        all[1]=new Goods("222",26);
        all[2]=new Goods("333",12);
        all[3]=new Goods("444",22);

        Arrays.sort(all);
        System.out.println(Arrays.toString(all));
    }
}

class Goods implements Comparable{
//属性
    private String name;
    private int price;
//构造器
    public Goods(String name, int price) {
        this.name = name;
        this.price = price;
    }

//get、set方法
//toString方法

//重写compareTo方法
    @Override
    public int compareTo(Object o) {
        if(o instanceof Goods){
            Goods gg = (Goods) o;
            if (this.price>gg.price){
                return 1;
            }else if(this.price<gg.price){
                return -1;
            }
            return 0;
        }

        throw new RuntimeException("输入数据类型不一致");
    }
}

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2.定制排序：java.util.Comparator

如果没有实现Comparable接口，可以考虑使用Comparator，重写compare方法，

Arrays.sort(goods，new comparator（）{

@Override

public int compare(Object o1，Object o2){

}

})；

package com.zkx.stringtest;

import java.util.Arrays;
import java.util.Comparator;

/**
 * @author zkx
 * @create 2022-02-11 22:35
 */
public class ComparatorTest {
    public static void main(String[] args) {
        Good [] goods = new Good[4];
        goods[0]= new Good("666",22);
        goods[1]= new Good("222",21);
        goods[2]= new Good("111",2);
        goods[3]= new Good("444",33);

        Arrays.sort(goods, new Comparator(){

            @Override
            public int compare(Object o1, Object o2) {
                Good g1 = (Good) o1;
                Good g2 = (Good) o2;

                return g1.getName().compareTo(g2.getName());

            }
        });

        System.out.println(Arrays.toString(goods));
    }
}

class Good {
    private String name;
    private int price;

    public Good(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 "Good{" +
                "name='" + name + '\'' +
                ", price=" + price +
                '}';
    }
}

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3.System类

https://blog.youkuaiyun.com/PorkBird/article/details/113695807

4.Math类

同上

5.BigInteger与BigDecimal

同上