JAVA排序的问题

发布网友发布时间：2022-05-12 07:25

共2个回答

热心网友时间：2023-01-25 04:23

有很多方法实现，我写了一个，你看看，可以按需求自己修改

package com.random;

import java.util.Comparator;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Set;
import java.util.TreeSet;

public class Client {
    public static void main(String[] args) {
        Set<Student> set = new HashSet<Student>();
        Student s1 = new Student(101, "刘备", "1班", 89.5f, 75f);
        Student s2 = new Student(106, "关羽", "1班", 78f, 69f);
        Student s3 = new Student(105, "张飞", "1班", 60.5f, 55f);
        Student s4 = new Student(104, "诸葛亮", "2班", 99.5f, 100f);
        Student s5 = new Student(103, "马超", "2班", 88.5f, 77f);
        Student s6 = new Student(102, "典韦", "3班", 88.5f, 88f);

        set.add(s1);
        set.add(s2);
        set.add(s3);
        set.add(s4);
        set.add(s5);
        set.add(s6);

        System.out.println("--------未排序-------");
        for(Student s : set){
            System.out.println("学号：" + s.getId() + "  姓名：" + s.getName() + "  班级：" + s.getClassName()
                    + "  java成绩：" + s.getJavaScore() + "  sql成绩：" + s.getSqlScore()
                    + "  总成绩：" + (s.getJavaScore() + s.getSqlScore()) + " \n");
        }

        System.out.println("--------按学号升序排列-------");
        Set<Student> ascId = new TreeSet<Student>(getComparator("id", 0));
        ascId.addAll(set);
        for(Student s : ascId){
            System.out.println("学号：" + s.getId() + "  姓名：" + s.getName() + "  班级：" + s.getClassName()
                    + "  java成绩：" + s.getJavaScore() + "  sql成绩：" + s.getSqlScore()
                    + "  总成绩：" + (s.getJavaScore() + s.getSqlScore()) + " \n");
        }

        System.out.println("--------按学号降序排列-------");
        Set<Student> descId = new TreeSet<Student>(getComparator("id", 1));
        descId.addAll(set);
        for(Student s : descId){
            System.out.println("学号：" + s.getId() + "  姓名：" + s.getName() + "  班级：" + s.getClassName()
                    + "  java成绩：" + s.getJavaScore() + "  sql成绩：" + s.getSqlScore()
                    + "  总成绩：" + (s.getJavaScore() + s.getSqlScore()) + " \n");
        }

        System.out.println("--------按java成绩降序排列-------");
        Set<Student> descJava = new TreeSet<Student>(getComparator("javaScore", 1));
        descJava.addAll(set);
        for(Student s : descJava){
            System.out.println("学号：" + s.getId() + "  姓名：" + s.getName() + "  班级：" + s.getClassName()
                    + "  java成绩：" + s.getJavaScore() + "  sql成绩：" + s.getSqlScore()
                    + "  总成绩：" + (s.getJavaScore() + s.getSqlScore()) + " \n");
        }

        System.out.println("--------按sql成绩降序排列-------");
        Set<Student> descSQL = new TreeSet<Student>(getComparator("sqlScore", 1));
        descSQL.addAll(set);
        for(Student s : descSQL){
            System.out.println("学号：" + s.getId() + "  姓名：" + s.getName() + "  班级：" + s.getClassName()
                    + "  java成绩：" + s.getJavaScore() + "  sql成绩：" + s.getSqlScore()
                    + "  总成绩：" + (s.getJavaScore() + s.getSqlScore()) + " \n");
        }

        System.out.println("--------按总分降序排列-------");
        Set<Student> descAVG = new TreeSet<Student>(getComparator("avgScore", 1));
        descAVG.addAll(set);
        for(Student s : descAVG){
            System.out.println("学号：" + s.getId() + "  姓名：" + s.getName() + "  班级：" + s.getClassName()
                    + "  java成绩：" + s.getJavaScore() + "  sql成绩：" + s.getSqlScore()
                    + "  总成绩：" + (s.getJavaScore() + s.getSqlScore()) + " \n");
        }

        System.out.println("--------各班的java成绩平均分-------");
        Set<Entry<String, Float>> javaScore = groupByClass(set, "java").entrySet();
        for(Entry<String, Float> score : javaScore){
            System.out.println("班级：" + score.getKey() + " 平均成绩：" + score.getValue() + " \n");
        }

        System.out.println("--------各班的sql成绩平均分-------");
        Set<Entry<String, Float>> sqlScore = groupByClass(set, "sql").entrySet();
        for(Entry<String, Float> score : sqlScore){
            System.out.println("班级：" + score.getKey() + " 平均成绩：" + score.getValue() + " \n");
        }
    }

    //condition：按那个条件排序，order=0 升序，order为其他降序
    public static Comparator<Student> getComparator(String condition, final int order){
        if("id".equals(condition)){
            return new Comparator<Student>(){
                @Override
                public int compare(Student s1, Student s2) {
                    if(order == 0){
                        return (s1.getId() > s2.getId() ? 1 : -1);

                    }else{
                        return (s1.getId() > s2.getId() ? -1 : 1);
                    }
                }
            };

        }else if("javaScore".equals(condition)){
            return new Comparator<Student>(){
                @Override
                public int compare(Student s1, Student s2) {
                    if(order == 0){
                        return (s1.getJavaScore() > s2.getJavaScore() ? 1 : -1);

                    }else{
                        return (s1.getJavaScore() > s2.getJavaScore() ? -1 : 1);
                    }
                }
            };

        }else if("sqlScore".equals(condition)){
            return new Comparator<Student>(){
                @Override
                public int compare(Student s1, Student s2) {
                    if(order == 0){
                        return (s1.getSqlScore() > s2.getSqlScore() ? 1 : -1);

                    }else{
                        return (s1.getSqlScore() > s2.getSqlScore() ? -1 : 1);
                    }
                }
            };

        }else{
            return new Comparator<Student>(){
                @Override
                public int compare(Student s1, Student s2) {
                    if(order == 0){
                        return ((s1.getJavaScore() + s1.getSqlScore()) > (s2.getJavaScore() + s2.getSqlScore()) ? 1 : -1);

                    }else{
                        return ((s1.getJavaScore() + s1.getSqlScore()) > (s2.getJavaScore() + s2.getSqlScore()) ? -1 : 1);
                    }
                }
            };
        }
    }

    public static Map<String, Float> groupByClass(Set<Student> st, String subject ){
        Map<String, Float> map = new HashMap<String, Float>();
        //java成绩平均分
        if("java".equals(subject)){
            for(Student s : st){
                Float scort = map.get(s.getClassName());
                if(scort != null){
                    map.put(s.getClassName(), (scort + s.getJavaScore())/2);

                }else{
                    map.put(s.getClassName(), s.getJavaScore());
                }
            }
        //sql成绩平均分
        }else{
            for(Student s : st){
                Float scort = map.get(s.getClassName());
                if(scort != null){
                    map.put(s.getClassName(), (scort + s.getSqlScore())/2);

                }else{
                    map.put(s.getClassName(), s.getSqlScore());
                }
            }
        }
        return map;
    }
}

class Student {
    private long id;         //学号
    private String name;       //姓名
    private String className;  //班级名称
    private float javaScore;
    private float sqlScore;

    public Student(long id, String name, String className,
            float javaScore, float sqlScore){
        this.id = id;
        this.name = name;
        this.className = className;
        this.javaScore = javaScore;
        this.sqlScore = sqlScore;
    }

    public Student(){};

    public long getId() {
        return id;
    }

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

    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public String getClassName() {
        return className;
    }
    public void setClassName(String className) {
        this.className = className;
    }
    public float getJavaScore() {
        return javaScore;
    }
    public void setJavaScore(float javaScore) {
        this.javaScore = javaScore;
    }
    public float getSqlScore() {
        return sqlScore;
    }
    public void setSqlScore(float sqlScore) {
        this.sqlScore = sqlScore;
    }
}

追问Student1 s1 = new Student1(101, "刘备", "1班", 89.5f, 75f);

这里的信息是我们自己输入的，不是固定的，我在输入的时候后面会把前面的覆盖，您能把上面的改成手动输入的吗，谢谢！

热心网友时间：2023-01-25 05:41

select top 5 学号, 姓名, 班级, java成绩, SQL成绩, java成绩 + SQL成绩 as 总分 from Student
order by 学号, java成绩, SQL成绩, 总分

select 班级, avg(java成绩) as java成绩平均分, avg(Sql成绩) as Sql成绩平均分 from Student
group by 班级

求采纳追问我是要用java做而不是用数据库，谢谢