Java实验十二

1、编写学生类，该类定义了 3 个属性：学号、姓名、成绩。可以通过构造方法设置 3 个属性的内容，并覆写 Object 类中的 toString()方法，在 List 集合中加入 5 个学生对象，并将内容输出，之后使用比较器将对象的内容进行排序并显示在屏幕上。

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

public class Main {
    public static void main(String[] args) {
        List<Student> list = new ArrayList<>();
        list.add(new Student("002", "张三", 80));
        list.add(new Student("004", "李四", 90));
        list.add(new Student("003", "王五", 70));
        list.add(new Student("001", "赵六", 90));
        list.add(new Student("005", "钱七", 90));
        System.out.println("排序前：");
        for (Student student : list) {
            System.out.println(student);
        }
        Collections.sort(list);
        System.out.println("排序后：");
        for (Student student : list) {
            System.out.println(student);
        }
    }
}

class Student implements Comparable<Student> {
    private String id;
    private String name;
    private int score;

    public Student(String id, String name, int score) {
        this.id = id;
        this.name = name;
        this.score = score;
    }

    public String getId() {
        return id;
    }

    public void setId(String id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

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

    public int getScore() {
        return score;
    }

    public void setScore(int score) {
        this.score = score;
    }

    @Override
    public String toString() {
        return "Student{" +
                "id='" + id + '\'' +
                ", name='" + name + '\'' +
                ", score=" + score +
                '}';
    }

    @Override
    public int compareTo(Student stu) {
        if (this.id.compareTo(stu.id) > 0) {
            return 1;
    }else if(this.id.compareTo(stu.id) < 0){
            return -1;
        }else {
            if(this.score > stu.score){
                return -1;
        }else if (this.score < stu.score){
                return 1;
            }else {
                return 0;
            }
        }
    }
}

2、完成一个学生管理程序，使用学号作为键添加 5 个学生对象，并可以将全部的信息保存在文件中，可以实现对学生信息的学号查找、输出全部学生信息的功能。

import java.io.*;
import java.util.*;

public class Main {
    public static void main(String[] args) throws Exception{
        File file = new File("student.txt");
        OutputStream out = new FileOutputStream(file);
        Map<String,Student> map = new HashMap<String,Student>();
        map.put("1",new Student(2020001,"张三",91));
        map.put("2",new Student(2022008,"李四",92));
        map.put("3",new Student(2019003,"王五",99));
        map.put("4",new Student(2022002,"赵六",90));
        map.put("5",new Student(2021002,"田七",95));
        String str = map.toString();
        byte[] bytes = str.getBytes();
        out.write(bytes);
        out.close();
        Student val = map.get("1");
        System.out.println("1号学生的信息是："+val);
        System.out.println("所有学生的信息是：");
        Collection<Student> values = map.values();
        Iterator<Student> iter = values.iterator();
        while (iter.hasNext()) {
            Student stu = iter.next();
            System.out.println(stu);
        }
    }
}

class Student{
    private int num;
    private String name;
    private float score;
    public Student(int num,String name,float score){
        this.num=num;
        this.name=name;
        this.score=score;
    }

    @Override
    public String toString() {
        return "Student{" +
                "num=" + num +
                ", name='" + name + '\'' +
                ", score=" + score +
                '}';
    }

    public int getNum() {
        return num;
    }

    public void setNum(int num) {
        this.num = num;
    }

    public String getName() {
        return name;
    }

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

    public float getScore() {
        return score;
    }

    public void setScore(float score) {
        this.score = score;
    }
}

3、编写一个双向链表。

代码实现见：https://blog.csdn.net/qq_58284486/article/details/123531837

//代码实现见：https://blog.csdn.net/qq_58284486/article/details/123531837
class ListNode {
    public int val;
    public ListNode next;//前驱信息
    public ListNode prev;//后继信息

    public ListNode(int val) {
        this.val = val;
    }
}
public class DoubleLinkedList {
    public ListNode head;//标记双向链表的头结点
    public ListNode last;//标记双向链表的尾结点

    //头插法
    public void addFirst(int data) {
        ListNode node = new ListNode(data);
        if(this.head == null) {
            this.head = node;
            this.last = node;
        } else {
            node.next = this.head;
            this.head.prev = node;
            this.head = node;
        }
    }

    //尾插法
    public void addLast (int data) {
        ListNode node = new ListNode(data);
        if(this.head == null) {
            this.head = node;
            this.last = node;
        } else {
            this.last.next = node;
            node.prev = this.last;
            this.last = node;
        }
    }

    //寻找要插入的位置
    public ListNode findIndex(int index) {
        int pos = 0;
        ListNode cur = this.head;
        while(pos != index) {
            cur = cur.next;
            pos++;
        }
        return cur;
    }
    //指定位置插入key
    public void addIndex(int index, int data) {
        if(index < 0 || index > size()) {
            throw new RuntimeException("操作位置不合法");
        }
        if(index == 0) {
            addFirst(data);
            return;
        }

        if(index == size()) {
            addLast(data);
            return;
        }
        ListNode node = new ListNode(data);
        ListNode cur = findIndex(index);
        cur.prev.next = node;
        node.prev = cur.prev;
        node.next = cur;
        cur.prev = node;
    }

    //判断双向链表是否包含关键字key
    public boolean contains(int key) {
        ListNode cur = this.head;
        while(cur != null) {
            cur = cur.next;
            if(cur.val == key) {
                return true;
            }
        }
        return false;
    }

    //打印双向链表,正向打印
    public void display() {
        ListNode cur = this.head;
        while (cur != null) {
            System.out.print(cur.val+" ");
            cur = cur.next;
        }
    }

    //打印双向链表,反向打印
    public void display1() {
        ListNode cur = this.last;
        while(cur != null) {
            System.out.print(cur.val+" ");
            cur = cur.prev;
        }
    }

    //按值查找结点位置
    public ListNode findKeyIndex(int key) {
        ListNode cur = this.head;
        while(cur != null) {
            if(cur.val == key) {
                return cur;
            }
            cur = cur.next;
        }
        return null;
    }

    //删除第一次出现关键字为key的节点
    public void remove(int key) {
        if(this.head == null) {
            throw new RuntimeException("链表为空，无法进行删除操作");
        }
        if(this.head.val == key) {
            this.head = this.head.next;
            this.head.prev = null;
            return;
        }
        ListNode cur = findKeyIndex(key);
        if(cur == last) {
            this.last = this.last.prev;
            this.last.next = null;
            return;
        }
        cur.prev.next = cur.next;
        cur.next.prev = cur.prev;
    }

    //删除所有值为key的节点
    public void removeAll(int key) {
        if(this.head == null) {
            throw new RuntimeException("链表为空，无法进行删除操作");
        }
        ListNode cur = this.head.next;
        while(cur != this.last) {
            if(cur.val == key) {
                cur.prev.next = cur.next;
                cur.next.prev = cur.prev;
            }
            cur = cur.next;
        }
        if(this.head.val == key) {
            this.head = this.head.next;
            this.head.prev = null;
        }
        if(this.last.val == key) {
            this.last = this.last.prev;
            this.last.next = null;
        }
    }

    //得到单链表的长度
    public int size() {
        ListNode cur = this.last;
        int size = 0;
        while(cur != null) {
            cur = cur.prev;
            size++;
        }
        return size;
    }

    //清空单链表
    public void clear(){
        this.head = null;
        this.last = null;
    }

}

测试：

public class Main {
    public static void main(String[] args) {
        System.out.println("头插法");
        DoubleLinkedList dllFirst = new DoubleLinkedList();  //创建双向链表对象,头插法
        for(int i = 0; i < 10; i++) {
            dllFirst.addFirst(i);
        }
        System.out.println("链表长度为：" + dllFirst.size());
        dllFirst.display();
        System.out.println();
        System.out.println("在1号位置插入10086:");
        dllFirst.addIndex(1, 10086);
        dllFirst.display();
        System.out.println();
        System.out.println("是否包含10086?");
        System.out.println(dllFirst.contains(10086));
        System.out.println("10086的节点位置在:"+dllFirst.findKeyIndex(10086));
        System.out.println("删除10086");
        dllFirst.removeAll(10086);
        dllFirst.display();
    }
}

4、编程通过栈的方式将任意输入的字符串内容进行逆序输出。

import java.util.Stack;
public class Main {
    public static void main(String[] args) {
        Stack<String> stack = new Stack<String>();
        stack.push("人!");
        stack.push("先");
        stack.push("你");
        stack.push("日");
        stack.push("我");
        stack.push("山本");
        while (!stack.isEmpty()) {
            System.out.print(stack.pop());
        }
    }
}