Java异常处理+常用类+泛型

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//ProductTypeException异常类：
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public class ProductTypeException extends Exception{
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    private String message = "没有这个商品";
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    public void warn(){
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        System.out.println(message);
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    }
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}
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//FruitShop类：
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public class FruitShop {
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    String[] products = new String[]{"apple" , "banana"};
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    boolean findProduct(String s){
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        for( int i = 0 ; i < products.length ; i ++ ){
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            if( products[i].equals(s) )return true ;
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        }
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        return false ; // 处理异常
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    }
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    void purchase(String s) throws ProductTypeException{ //和异常类绑定的方法
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        if( !findProduct(s) ){
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            throw new ProductTypeException(); //方法内抛出对应异常实体
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        }
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        else {
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            //……
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        }
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    }
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    void purchaseWithoutThrows(String s){
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        if( !findProduct(s) ){
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            try {
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                throw new ProductTypeException(); //通过try抛出异常实体
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            }catch (ProductTypeException e){
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                e.warn();
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            }
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        }
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        else{
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            //……
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        }
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    }
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}
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//Main类：
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public class Main {
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    public static void main(String[] args){
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        FruitShop fruitShop = new FruitShop();
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        try{
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            fruitShop.purchase("beef");
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        }catch (ProductTypeException e){
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            e.warn();
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        }
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        fruitShop.purchaseWithoutThrows("beef");
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    }
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}

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public class Adder {
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    private long sum = 0;
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    Adder accumulate(int n){
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        this.sum += n ;
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        return this;
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    }
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    Adder multiply(int n){
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        this.sum *= n ;
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        return this;
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    }
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    long getSum(){
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        return this.sum;
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    }
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}
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public class MainClass {
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    public static void main(String[] args){
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        Adder adder = new Adder();
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        adder.accumulate(3).accumulate(5).multiply(2);
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        System.out.println(adder.getSum());
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        Adder otherAdder = new Adder();
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        otherAdder.accumulate(1).multiply(1).multiply(2).multiply(3); //3的阶乘
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        System.out.println(otherAdder.getSum());
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    }
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}

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public class Example<T> {
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    Object[] array = new Object[100] ; //集合最大时100个元素
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    private Integer total = 0 ;
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    void add(T e){
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        array[total] = e ;
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        total ++ ;
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    }
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    int length(){
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        return total ;
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    }
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    void output(){
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        for( int i = 0 ; i < total ; i ++ ){
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            System.out.print(array[i] + " ");
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        }
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        System.out.println();
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    }
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}
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public class Main {
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    public static void main(String[] args){
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        Example<String> es = new Example<>();
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        es.add("hello");
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        es.add("world");
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        es.add("!");
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        System.out.println(es.length());
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        es.output();
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    }
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}

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import java.util.ArrayList;
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import java.util.List;
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public class Product {
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    String name ;
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    Double price ;
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    Product(){}
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    Product(String name , Double price){
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        this.name = name ;
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        this.price = price ;
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    }
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}
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public class FruitShop {
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    List<Product> list = new ArrayList<>();
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    void addProduct(Product product){ //增添商品
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        list.add(product);
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    }
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    int returnTypes(){ //返回一共有多少种商品
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       return list.size();
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    }
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    Product getNthGoods(int index){ //获取第n个商品
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        return list.get(index);
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    }
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    void setNthGoods(int index , Product product){ //修改第n个商品的信息
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        list.set(index , product);
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    }
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} //感觉只是给list的各种方法改了个名……
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public class Main {
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    public static void main(String[] args){
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        FruitShop fruitShop = new FruitShop();
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        fruitShop.addProduct(new Product("apple" , 3.14));
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        fruitShop.addProduct(new Product("banana" , 5.20));
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        System.out.println("共有" + fruitShop.returnTypes() + "种商品");
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        System.out.println("第1个水果是:" + fruitShop.getNthGoods(0).name + "价格:" + fruitShop.getNthGoods(0).price );
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        fruitShop.setNthGoods(0 , new Product("applePlus" , 10.0 ));
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        System.out.println("修改后:");
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        System.out.println("第1个水果是:" + fruitShop.getNthGoods(0).name + "价格:" + fruitShop.getNthGoods(0).price );
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        System.out.println("第1个水果是:" + fruitShop.getNthGoods(1).name + "价格:" + fruitShop.getNthGoods(1).price );
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    }
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}

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import java.util.*;
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public class Main {
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    public static void main(String[] args){
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        Set<Integer> s1 = new HashSet<>(); // 无序
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        Set<Integer> s2 = new LinkedHashSet<>(); // 按插入顺序排序
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        Set<Integer> s = new TreeSet<>(); // 有序，默认升序
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        //下面拿TreeSet的实现举例
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        s.add(10);
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        s.add(2);
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        s.add(5);
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        s.add(20);
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        s.add(18);
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        //此时s内：2 5 10 18 20
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        for( Iterator<Integer> it = s.iterator() ; it.hasNext() ; ){
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            System.out.println(it.next());
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        } // 输出s
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    }
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}

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import java.util.*;
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public class Student implements Comparable<Student>{
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    String name = null ;
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    Integer grade = null ;
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    Student(){}
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    Student(String name , Integer grade){
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        this.name = name ;
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        this.grade = grade ;
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    }
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    @Override
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    public int compareTo(Student student) {
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        if(this.grade != student.grade)
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            return student.grade - this.grade ; //成绩高的放在前面
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        else return this.name.compareTo(student.name); // 姓名小的放在前面
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    } //此处必须写else一行，否则对于成绩相等的同学，会被认为是同一个元素
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}
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public class Main {
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    public static void main(String[] args){
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        Set<Student> s = new TreeSet<>();
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        s.add(new Student("zhangsan",99));
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        s.add(new Student("lisi",100));
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        s.add(new Student("wangwu",98));
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        s.add(new Student("zhaoliu",99));
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        for( Student student : s ){
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            System.out.println(student.name + " " + student.grade);
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        }
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    }
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}

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import java.util.*;
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public class Product implements Comparable<Product>{
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    String name ;
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    Double price ;
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    Product(){}
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    Product(String name , Double price){
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        this.name = name ;
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        this.price = price ;
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    }
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    @Override
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    public int compareTo(Product product) {
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        return this.name.compareTo(product.name);
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    } //将名称按字典序排序
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}
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public class FruitShop {
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    Set<Product> set = new TreeSet<>();
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    void addProduct(Product product){
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        set.add(product);
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    }
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    int returnTypes(){
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        return set.size();
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    }
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    boolean contains(Product product){
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        return set.contains(product);
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    }
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}
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public class Main {
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    public static void main(String[] args){
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        FruitShop fruitShop = new FruitShop();
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        fruitShop.addProduct(new Product("apple" , 3.14));
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        fruitShop.addProduct(new Product("banana" , 5.20));
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        System.out.println("初始");
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        for(Product product : fruitShop.set){
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            System.out.println(product.name + " " + product.price);
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        }
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        Set<Product> trunk = new TreeSet<>(); //进货
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        trunk.add(new Product("mango",5.8));
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        trunk.add(new Product("pear",4.5));
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        fruitShop.set.addAll(trunk);
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        System.out.println("进货后");
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        for(Product product : fruitShop.set){
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            System.out.println(product.name + " " + product.price);
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        }
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        Set<Product> buyer = new TreeSet<>(); //大买家
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        buyer.add(new Product("banana" , 5.20));
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        buyer.add(new Product("pear",4.5)); //买光所有的banana和pear
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        fruitShop.set.removeAll(buyer);
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        System.out.println("购买后");
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        for(Product product : fruitShop.set){
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            System.out.println(product.name + " " + product.price);
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        }
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    }
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}

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import java.util.*;
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public class Main {
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    public static void main(String[] args){
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        // 我们还是以默认按key升序的TreeMap举例
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        Map<String , Double> fruitShop = new TreeMap<>();
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        fruitShop.put("apple" , 3.14);
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        fruitShop.put("banana" , 5.20);
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        System.out.println("店里有:");
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        for( String key : fruitShop.keySet() ){
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            System.out.println(key + " " + fruitShop.get(key));
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        }
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        System.out.println("一共" + fruitShop.size() + "种水果");
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        if(fruitShop.containsKey("mango")) System.out.println("有mango");
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        else System.out.println("没有mango");
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        if(fruitShop.containsValue(3.14)) System.out.println("有3.14元的水果");
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        else System.out.println("没有3.14元的水果");
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    }
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}