[英]How to read a file containing strings and integers into an ArrayList and sort by integer?
我正在尝试从包含按行组织的名称和等级列表的文本文件中读取,即:
大卫·史密斯84
苏珊L波特100
...
然后将它们(按行)存储在ArrayList中,并使用选择排序算法按学生的成绩对该ArrayList进行排序,但是我尝试了多种不同的方式对此进行编码,并且每次编辑似乎都提示另一个错误(我非常编程新手)。 这是我目前拥有的:
import java.io.*;
import java.util.*;
public class Grades {
private static void sort(ArrayList<String> list) {
int pFill;
int pTest;
int pSmallest;
String temp;
for (pFill = 0; pFill < list.size(); pFill++) {
pSmallest = pFill;
for (pTest = pFill + 1; pTest < list.size(); pTest++) {
if (pTest < pSmallest) {
pSmallest = pTest;
}
}
temp = list.get(pSmallest);
list.set(pSmallest, list.get(pFill));
list.set(pFill, temp);
}
}
public static void main(String[] args){
ArrayList<String> list = new ArrayList<>();
String fileName = "students.txt";
try (BufferedReader input = new BufferedReader(new FileReader(fileName))) {
while(input.ready()){
list.add(input.readLine());
}
input.close();
sort(list);
System.out.println(list);
} catch (IOException e){
System.out.println(e.getMessage());
}
}
}
如果您声明一个带有两个字段name
和age
的Student
类将很容易。 您可以使Student
班级实现Comparable
并根据年级进行比较。 它看起来像这样:
public class Student implements Comparable<Student> {
private final String name;
private final int grade;
public Student(String name, int grade) {
this.name = name;
this.grade = grade;
}
@Override
public int compareTo(Student s) {
return Integer.compare(this.grade, grade);
}
}
要填充Student
对象,您将需要拆分String
并提取名称和等级,然后调用new Student(name, grade)
。
在您的sort
方法中,您可以传递List<Student>
,您可以在其中通过调用s1.compareTo(s2)
来比较2个学生(由于Student implements Comparable<Student>
s1.compareTo(s2)
。
一旦获得学生名单。 您可以使用比较器来执行此操作。
List<Student> sorted=list.sort(Comparator.comparing(p-> p.getGrade()));
或使用流API
List<Person> result =list.stream().sorted((p1, p2)>p1.getGrade().compareTo(p2.getGrade())).collect(Collectors.toList());
您可以创建一个学生对象来分别保存姓名和等级。 一旦你添加了所有的数据到列表中,您可以直接使用list.sort()方法通过使用比较 ,但在你的情况,你要那种写的选择,这就是为什么你必须写另一种方法做选择排序。
package com.stackovflow.problems;
import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;
import java.util.ArrayList;
public class Grades {
public static void main(String[] args){
ArrayList<Student> list = new ArrayList<>();
String fileName = "students.txt";
try (BufferedReader input = new BufferedReader(new FileReader(fileName))) {
while(input.ready()){
String line = input.readLine().trim();
String name = line.substring(0,line.lastIndexOf(' '));
int grade = Integer.parseInt(line.substring(line.lastIndexOf(' ')+1));
list.add(new Student(name, grade));
}
input.close();
selectionSort(list);
System.out.println(list);
} catch (IOException e){
System.out.println(e.getMessage());
}
}
private static void selectionSort(ArrayList<Student> list) {
int pFill;
int pTest;
int pSmallest;
Student temp;
for (pFill = 0; pFill < list.size(); pFill++) {
pSmallest = pFill;
for (pTest = pFill + 1; pTest < list.size(); pTest++) {
Student pTestStudent = list.get(pTest);
Student pSmallestStudent = list.get(pSmallest);
if (pTestStudent.getGrade() < pSmallestStudent.getGrade()) {
pSmallest = pTest;
}
}
if(pSmallest!=pFill) {
temp = list.get(pSmallest);
list.set(pSmallest, list.get(pFill));
list.set(pFill, temp);
}
}
}
}
//This class is to hold line data in your students.txt file
class Student{
private String name;
private int grade;
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getGrade() {
return grade;
}
public void setGrade(int grade) {
this.grade = grade;
}
public Student(String name, int grade) {
super();
this.name = name;
this.grade = grade;
}
@Override
public String toString() {
return "Student [name=" + name + ", grade=" + grade + "]";
}
}
在同一文件夹中创建一个单独的Student.java文件,以保存Student类:
public class Student {
private final String name;
private final int grade;
public Student(String name, int grade) {
this.name = name;
this.grade = grade;
}
public String getName(){
return name;
}
public int getGrade(){
return grade;
}
}
然后将每行按空格分开,并将第一个标记设置为名称,将最后一个标记设置为成绩,然后使用Comparator对学生对象的ArrayList进行排序:
import java.io.*;
import java.util.*;
public class Grades {
private static ArrayList<Student> sort(ArrayList<String> list) {
ArrayList<Student> students = new ArrayList<Student>();
String name = "";
int grade;
for (String line : list) {
String[] splitted = line.split("\\s+");
for(int i = 0;i< splitted.length-1;i++){
name += splitted[i] + " ";
}
grade = Integer.parseInt(splitted[splitted.length-1]);
students.add(new Student(name,grade));
name = "";
}
students.sort(Comparator.comparing(student-> student.getGrade()));
return students;
}
public static void main(String[] args){
ArrayList<String> list = new ArrayList<>();
String fileName = "students.txt";
try (BufferedReader input = new BufferedReader(new FileReader(fileName))) {
while(input.ready()){
list.add(input.readLine());
}
input.close();
ArrayList<Student> sortedStudents = sort(list);
for (Student currentStudent : sortedStudents)
System.out.println(currentStudent.getName() + currentStudent.getGrade());
} catch (IOException e){
System.out.println(e.getMessage());
}
}
}
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