Question

我想从arraylist中添加，更新和删除元素。由于我是Java新手或任何类型的编程，我无法在谷歌搜索后找出整个解决方案。我可以添加元素到arrayList。以下是我的代码：

import java.util.ArrayList;
import java.util.Scanner;


public class Main {

/**
 * @param args
 */
public static void main(String[] args) {
    Scanner scan = new Scanner(System.in);
    ArrayList<Student> someStudent = new ArrayList<Student>();
    char quit = 'Y';
     int id;
     String name;
     float cgpa;

     while(quit == 'Y'){
         System.out.print("\n ID: ");
         id=scan.nextInt();

         System.out.print("\n Name: ");
         name=scan.next();

         System.out.print("\n CGPA: ");
         cgpa=scan.nextFloat();

         someStudent.add (new Student(id, name, cgpa));
         System.out.print(" Enter Another Record? (Y/N)");
         String word = scan.next();
         word = word.toUpperCase();
         quit= word.charAt(0);
         //scan.close();
     }

     for(Student student:someStudent){
         System.out.println(student.id);
         System.out.println(student.name);
         System.out.println(student.cgpa);
     }
     }
     }

Student.java：

public class Student {

    public int id;
    public String name;
    public float cgpa;
    //public String address;

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

}

代码输出：

ID: 1

 Name: abc

 CGPA: 3.5
 Enter Another Record? (Y/N)y

 ID: 2

 Name: def

 CGPA: 2.6
 Enter Another Record? (Y/N)y

 ID: 3

 Name: xyz

 CGPA: 4.0
 Enter Another Record? (Y/N)n
1
abc
3.5
2
def
2.6
3
xyz
4.0

我的问题是如何从该arraylist中搜索元素并更新或删除它们。

Answer 1

您可以尝试这样的事情：

System.out.print("Select student by ID: ";
int pickID = scan.nextInt();
boolean found = false;
for(Student s : someStudent){
    if(s.id == pickID && !found){
        update(s);
        found = true;
    }
}
if(!found){
    System.out.println("No student with that ID.");
}

更新方法

public void update(Student s){
    boolean edit = true;
    while(edit){
        System.out.println(String.format("Select operation:\n1. Change name\n2. Change ID\n3. Change CGPA\n4. Delete\n5. Done"));
        int opt = scan.nextInt();
        switch(opt){
            case 1:
                String newName = scan.next();
                s.setName(newName);
                break;
            case 2:
                int newID = scan.nextInt();
                s.setID(newID);
                break;
            case 3:
                float newCGPA = scan.nextFloat();
                s.setCGPA(newCGPA);
                break;
            case 4:
                for(int i=0;i<someStudent.length();i++){
                    if(someStudent.get(i)==s){
                        someStudent.remove(i);
                    }
                }
                break;
            case 5:
                edit = false;
                break;
            default:
                break;
        }
    }
}

向Student class

添加方法

public void setID(int id){this.id=id;}
public void setName(String name){this.name=name;}
public void setCGPA(float cgpa){this.cgpa=cgpa;}

Answer 2

根据您想要搜索的内容（我猜名称不是唯一的，ID是cgpa怎么样？）您应该使用Map而不是列表。因此，您将能够根据该地图中的唯一键找到学生。

运行时添加/删除/更新Arraylist在Java中

2 个答案: