课下作业2

课下作业

相关知识点的总结

• LinkedList泛型类
• mylist.add("String")添加节点,这样的节点是自动连在一起的，无需操作安排节点中的所存放的下一个或上一个节点的引用;
• public void add(int index,E element)向链表的指定位置添加一个新结点
• public E remove（int index）删除指定位置上的节点
• 迭代器

Iterator<Student> iter=list.iterator();
while(iter.hasNext()){
    Student stu=iter.next();
}

• 堆栈：public E push(E item);压栈操作，public E pop()弹栈操作

课上内容补做

任务二

针对下面的Student类，使用Comparator编程完成以下功能：

1. 在测试类StudentTest中新建学生列表，包括自己和学号前后各两名学生，共5名学生,给出运行结果（排序前，排序后）
2. 对这5名同学分别用学号和总成绩进行增序排序，提交两个Comparator的代码

import java.util.*;
class Test {
    public  static void main(String[] args) {
        List<Student> list = new LinkedList<>();
        list.add(new Student(20165206,"谭笑","male",19,86,88,89));
        list.add(new Student(20165207,"李天林","male",20,89,80,90));
        list.add(new Student(20165208,"孔月","male",19,95,97,91));
        list.add(new Student(20165209,"陈思兵","male",20,79,81,92));
        list.add(new Student(20165210,"刘宇坤","male",20,72,93,80));
        System.out.println("排序前的数据：");
        for (Student student : list) {
            System.out.println(student);
        }                                              
        SortByID sortByID = new SortByID();            
        Collections.sort(list, sortByID);
        System.out.println("根据学号由低到高排序：");
        for (Student student : list) {
            System.out.println(student);
        }
        SortByTotal_score sortBytotal_score = new SortByTotal_score();
        Collections.sort(list, sortBytotal_score);
        System.out.println("根据学生成绩由低到高排序：");
        for (Student student : list) {
            System.out.println(student);
        }
    }
}
class Student {          
    private int id;
    private String name;
    private int age;
    private String sex;
    private double computer_score;
    private double english_score;
    private double maths_score;
    private double total_score;
    private double ave_score; 

    @Override
    public String toString() {
        return "Student[name:"+name+",age:"+age+",number:"+id+",total_score"+total_score+"]";
    }

    public Student(int id, String name, String sex, int age,double computer_score,
                   double english_score,double maths_score) {
        this.id = id;
        this.name = name;
        this.sex = sex;
        this.age = age;
        this.computer_score = computer_score;
        this.english_score = english_score;
        this.maths_score = maths_score;
    }

    public int getId() {
        return id;
    }//获得当前对象的学号，

    public double getComputer_score() {
        return computer_score;
    }//获得当前对象的计算机课程成绩,

    public double getMaths_score() {
        return maths_score;
    }//获得当前对象的数学课程成绩,

    public double getEnglish_score() {
        return english_score;
    }//获得当前对象的英语课程成绩,

    public void setId(int id) {
        this.id = id;
    }// 设置当前对象的id值,

    public void setComputer_score(double computer_score) {
        this.computer_score = computer_score;
    }//设置当前对象的Computer_score值,

    public void setEnglish_score(double english_score) {
        this.english_score = english_score;
    }//设置当前对象的English_score值,

    public void setMaths_score(double maths_score) {
        this.maths_score = maths_score;
    }//设置当前对象的Maths_score值,

    public double getTotalScore() {
        total_score=computer_score + maths_score + english_score;
        return total_score;
    }// 计算Computer_score, Maths_score 和English_score 三门课的总成绩。

    public double getAveScore() {
        return getTotalScore() / 3;
    }// 计算Computer_score, Maths_score 和English_score 三门课的平均成绩。

}

class SortByID implements Comparator<Student> {

    @Override
    public int compare(Student o1, Student o2) {
        return o1.getId() - o2.getId();
    }

}
class SortByTotal_score implements Comparator<Student> {

    @Override
    public int compare(Student o1, Student o2) {
        return (int)( o1.getTotalScore() - o2.getTotalScore());
    }
}

运行截图如下

任务三

参见附件，补充MyList.java的内容

import java.util.*;
public class MyList {
    public static void main(String [] args) {
        LinkedList mylist=new LinkedList();
        mylist.add("20165206");
        mylist.add("20165207");
        mylist.add("20165209");
        mylist.add("20165210");
        for(int i=0;i<4;i++){
            String temp=(String)mylist.get(i);
            System.out.println("第"+i+"节点中的数据:"+temp);
        }

        mylist.add(2,"20165208");
        for(int i=0;i<5;i++){
            String temp=(String)mylist.get(i);
            System.out.println("第"+i+"节点中的数据:"+temp);
        }

        mylist.remove("20165208");
        for(int i=0;i<4;i++){
            String temp=(String)mylist.get(i);
            System.out.println("第"+i+"节点中的数据:"+temp);
        }
    }
}

问题反思

本次测试出现的问题一是还不够熟练，在任务二时只匆匆完成了一步，没有完成试验要求；二是在使用方法 mylist.add(2,20165208)时错把关键词的顺序写错，正确输入应为前者为指定位置后者为指定数据;三是在课下进行修改时发现直接利用mylist.remove(2)无法实现实验目的，他会将后续所有结点一并删除。除此之外还有一个错误是未将关键词用“”引上，导致输入失败，而无法显示第二步的插入。

补做教材第十五章的编程题目

• 使用堆栈结构输出an的若干项，其中an=2an-1+2an-2，a1=3，a2=8

import java.util.*;
public class Ex {
    public static void main(String args[]) {
        Stack<Integer> stack=new Stack<Integer>();
        stack.push(new Integer(3));
        stack.push(new Integer(8));
        int k=1;
        while(k<=8) {
                Integer F1=stack.pop();
                int f1=F1.intValue();
                Integer F2=stack.pop();
                int f2=F2.intValue();
                Integer temp=new Integer(2*f1+2*f2);
                System.out.println(""+temp.toString());
                stack.push(temp);
                stack.push(F2);
                k++;
        }
    }
}

其中an的个数由k控制，实现效果如下图。

• 将链表中的学生英语成绩单存放到一个树集中，使得按成绩自动排序，并输出排序结果

import java.util.*;
class CollegeStu implements Comparable {
    int english=0;
    String name;
    CollegeStu(int english,String name) {
        this.name=name;
        this.english=english;
    }
    @Override
    public int compareTo(Object b) {
        CollegeStu stu=(CollegeStu)b;
        return (this.english-stu.english);
    }
}
public class Exam2 {
    public static void main(String[] args) {
        List<CollegeStu> list=new LinkedList<CollegeStu>();
        int score []={99, 88, 77, 66, 55};
        String name []={"谭笑","李天林","孔月","陈思兵" ,"刘宇坤"};
        for (int i=0;i<score.length;i++) {
            list.add(new CollegeStu(score[i],name[i]));
        }
        Iterator<CollegeStu> iter=list.iterator();
        TreeSet<CollegeStu> mytree=new TreeSet<CollegeStu>();
        while (iter.hasNext()) {
            CollegeStu stu=iter.next();
            mytree.add(stu);
            System.out.println(" "+stu.name+" "+stu.english);
        }

    }
}

• 有10个U盘，有两个重要的属性：价格和容量，编写一个应用程序，使用TreeMap<K,V>类，分别按照价格和容量排序输出10个U盘的详细信息

import java.util.*;
class UDiscKey implements Comparable {
    double key=0;
    UDiscKey(double d) {
        key=d;
    }
    public int compareTo(Object b) {
        UDiscKey disc=(UDiscKey)b;
        if((this.key-disc.key)==0)
            return -1;
        else
            return (int)((this.key-disc.key)*1000);
    }
}
class UDisc{
    int amount;
    double price;
    UDisc(int m,double e) {
        amount=m;
        price=e;
    }
}
public class Ex3 {
    public static void main(String args[ ]) {
        TreeMap<UDiscKey,UDisc>  treemap= new TreeMap<UDiscKey,UDisc>();
        int amount[]={1,2,4,8,16,32,64,128,256,512,1024};
        double price[]={40,20,10,80,300,220,380,400,600,500};
        UDisc UDisc[]=new UDisc[10];
        for(int k=0;k<UDisc.length;k++) {
            UDisc[k]=new UDisc(amount[k],price[k]);
        }
        UDiscKey key[]=new UDiscKey[10];
        for(int k=0;k<key.length;k++) {
            key[k]=new UDiscKey(UDisc[k].amount);        }
        for(int k=0;k<UDisc.length;k++) {
            treemap.put(key[k],UDisc[k]);                 }
        int number=treemap.size();
        Collection<UDisc> collection=treemap.values();
        Iterator<UDisc> iter=collection.iterator();
        while(iter.hasNext()) {
            UDisc disc=iter.next();
            System.out.println(""+disc.amount+"G "+disc.price+"元");       }
        treemap.clear();
        for(int k=0;k<key.length;k++) {
            key[k]=new UDiscKey(UDisc[k].price);       }
        for(int k=0;k<UDisc.length;k++) {
            treemap.put(key[k],UDisc[k]);       }
        number=treemap.size();
        collection=treemap.values();
        iter=collection.iterator();
        while(iter.hasNext()) {
            UDisc disc=iter.next();
            System.out.println(""+disc.amount+"G "+disc.price+"元");
        }
    }
}