JAVA集合练习

1.已知有一个Worker 类如下：

public class Worker {

private int age;

private String name;

private double salary;

public Worker (){

}

public Worker (String name, int age, double salary){

this.name = name;

this.age = age;

this.salary = salary;

}

public int getAge() { return age; }

public void setAge(int age) { this.age = age; }

public String getName() { return name; }

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

public double getSalary(){ return salary; }

public void setSalary(double salary){ this.salary = salary; }

public void work(){

System.out.println(name + “ work”);

}

}

完成下面的要求

1) 创建一个List，在List 中增加三个工人，基本信息如下：

姓名 年龄 工资

zhang3 18 3000

li4 25 3500

wang5 22 3200

2) 在li4 之前插入一个工人，信息为：姓名：zhao6，年龄：24，工资3300

3) 删除wang5 的信息

4) 利用for 循环遍历，打印List 中所有工人的信息

5) 利用迭代遍历，对List 中所有的工人调用work 方法。

        List<Worker> workers = new ArrayList<>();
        workers.add(new Worker("zhang3", 18, 3000));
        workers.add(new Worker("li4", 25, 3500));
        workers.add(new Worker("wang5", 22, 3200));
        System.out.println(workers);
        int index = 0;
        for (int i = 0; i < workers.size(); i++) {
            if (workers.get(i).getName().equals("li4")) {
                index = i;
            }
        }
        System.out.println("li4在集合中的下标：" + index);
        //插入zhao6
        workers.add(index, new Worker("zhao6", 24, 3300));
        System.out.println(workers);
        //删除wang5
        Iterator<Worker> it = workers.iterator();
        while (it.hasNext()){//是否有下一个元素
            Worker worker = it.next();//获取下一个元素
            if (worker.getName().equals("wang5")){
                it.remove();//必须使用迭代器的删除方法
//                workers.remove(worker);//运行时报错
            }
        }
        //for循环遍历
        System.out.println(workers);
        for (Worker worker:workers ) {
            System.out.println(worker);
        }
        //利用迭代器遍历
        Iterator<Worker> it2 = workers.iterator();
        while (it2.hasNext()){
            Worker worker = it2.next();
            worker.work();
        }

2.去除集合中字符串的重复值（要求使用 ArrayList）

执行结果如下：

旧集合为：[李玉伟, 李嘉诚, 马化腾, 刘强东, 李玉伟, 王健林, 马云, 雷军]

新集合为：[李玉伟, 李嘉诚, 马化腾, 刘强东, 王健林, 马云, 雷军]

        String[] strArr = {"李玉伟", "李嘉诚", "马化腾", "刘强东","李玉伟" , "王健林", "马云", "雷军"};
        //数组转集合
        List<String> list1 = Arrays.asList(strArr);
        //asList转化的底层代码不一样,重新接收一下,否则报错
        List<String> list = new ArrayList<>(list1);
//        Object[] object = list.toArray();//集合转 数组
        for (int i = 0; i < list.size(); i++) {
            for (int j = i+1; j < list.size(); j++) {
                if (list.get(i).equals(list.get(j))){
                    list.remove(j);
                    j--;//删除后往前移一位
                }
            }
        }
        System.out.println(list1);
        System.out.println(list);

3.分析以下需求，并用代码实现：(使用ArrayList)

(1)生成10个1至100之间的随机整数(不能重复)，存入一个List集合

(2)编写方法对List集合进行排序

(2)然后利用迭代器遍历集合元素并输出

(3)如：15 18 20 40 46 60 65 70 75 91

List<Integer> list = new ArrayList<>();
        while (list.size() < 10){
            int ranNum = new Random().nextInt(1,101);
            if (!list.contains(ranNum)){
                list.add(ranNum);
            }
        }
        System.out.println(list);
        System.out.println(list.size());
 
        List<Integer> sortList = sortList(list);
        System.out.println(sortList);
 
        Iterator<Integer> it = sortList.iterator();
        while (it.hasNext()){
            Integer i = it.next();
            System.out.print(i + " ");
        }
//排序方法-------------
    public static List<Integer> sortList(List<Integer> list){
        for (int i = 0; i < list.size()-1; i++) {
            for (int j = 0; j < list.size() - i - 1; j++) {
                if (list.get(j) > list.get(j+1)){
                    int temp = list.get(j);
                    list.set(j,list.get(j+1));
                    list.set(j+1,temp);
                }
            }
        }
        return list;
    }

4.编写一个类Book，具有name,price,press(出版社),author 然后创建5个对象放入ArrayList中，并实现按照price大小排序，

然后遍历ArrayList输出每个Book对象, 使用toString 方法打印。

        Book book1 = new Book("《从尸解仙开始》", 100.5, "起点中文网", "鳄鱼皮的皮");
        Book book2 = new Book("《光阴之外》", 200.5, "起点中文网", "耳根");
        Book book3 = new Book("《深空彼岸》", 180.5, "起点中文网", "辰东");
        Book book4 = new Book("《明克街13号》", 130.5, "起点中文网", "纯洁滴小龙");
        Book book5 = new Book("《灵境行者》", 210.5, "起点中文网", "卖报小郎君");
        List<Book> books = new ArrayList<>();
        books.add(book1);
        books.add(book2);
        books.add(book3);
        books.add(book4);
        books.add(book5);
        System.out.println(books);
 
        BookComparator bookComparator = new BookComparator();
        books.sort(bookComparator);
        System.out.println(books);
 
        System.out.println("------------");
        for (Book book : books) {
            System.out.println(book);
        }
 
//book类------------
public class Book {
    private String name;
    private double price;
    private String press;
    private String author;
 
    public Book() {
    }
 
    public Book(String name, double price, String press, String author) {
        this.name = name;
        this.price = price;
        this.press = press;
        this.author = author;
    }
 
    public String getName() {
        return name;
    }
 
    public void setName(String name) {
        this.name = name;
    }
 
    public double getPrice() {
        return price;
    }
 
    public void setPrice(double price) {
        this.price = price;
    }
 
    public String getPress() {
        return press;
    }
 
    public void setPress(String press) {
        this.press = press;
    }
 
    public String getAuthor() {
        return author;
    }
 
    public void setAuthor(String author) {
        this.author = author;
    }
 
    @Override
    public String toString() {
        return "Book{" +
                "name='" + name + '\'' +
                ", price=" + price +
                ", press='" + press + '\'' +
                ", author='" + author + '\'' +
                '}';
    }
}
 
//book比较方法------------
import java.util.Comparator;
 
// 定义 书类型的  比较器
public class BookComparator implements Comparator<Book> {
 
    @Override
    public int compare(Book b1, Book b2) {
        // 定义比较规则
        if (b1.getPrice() > b2.getPrice()){
            return 1;
        }else if (b1.getPrice() < b2.getPrice()){
            return -1;
        }
        return 0;
    }
}

5.使用List集合存储10个学生信息。

学生信息：姓名，年龄，成绩。

统计所有姓“张”的同学的平均成绩。

        List<Student> studentList = new ArrayList<>();
        studentList.add(new Student("张三", 20 , 90) );
        studentList.add(new Student("赵三", 23 , 67) );
        studentList.add(new Student("李三", 20 , 54) );
        studentList.add(new Student("张四", 20 , 87) );
        studentList.add(new Student("张二", 20 , 57) );
        studentList.add(new Student("张六", 20 , 87) );
        studentList.add(new Student("张七", 20 , 34) );
        studentList.add(new Student("王十一", 20 , 67) );
        studentList.add(new Student("王三", 20 , 98) );
        studentList.add(new Student("张三", 20 , 80) );
 
        double sumScore = 0; // 姓张的同学的总成绩
        int index = 0 ;// 姓张的同学的人数
        for (int i = 0; i < studentList.size(); i++) {
            if (studentList.get(i).getName().startsWith("张")){
                index ++; // 姓张的同学的人数 + 1
                sumScore += studentList.get(i).getScore();
            }
        }
        double avg = sumScore / index ;
        System.out.println("平均分：" + avg);

1. 产生10个1-100的随机数，并放到一个数组中，把数组中大于等于10的数字放到一个list集合中，并打印到控制台

        int[] arr = new int[10];
        List<Integer> list = new ArrayList<>();
        for (int i = 0; i < arr.length; i++) {
            arr[i] = (int)(Math.random() * 100 + 1);
            if (arr[i] > 10){
                list.add(arr[i]);
            }
        }
        System.out.println(Arrays.toString(arr));
        System.out.println(list);