“在arraylist构造函数中找不到适用于add(java.lang.String)的合适方法"? [英] "no suitable method found for add(java.lang.String)"in arraylist constructor?

问题描述

import java.util.ArrayList;
import java.util.Random;

    public class College
    {
        // instance variables - replace the example below with your own
        private ArrayList<Student> students;

    public College()
        {
            // initialise instance variables
            ArrayList<Student> students = new ArrayList<Student>();
            students.add("Student 1");
            students.add("Student 2");
            students.add("Student 3");

        }
    }

基本上，它突出显示了.add，显示了错误消息"java.lang.IllegalArgumentException:绑定必须为正"，我不明白我在这里做错了什么吗?我在这里查看了许多这类问题线程，但我确实做了他们所做的事情

basically it highlights the .add showing the error message "java.lang.IllegalArgumentException: bound must be positive", I don't understand what I did wrong here? I looked at a lot of these kinds of problem threads here but I did exactly what they did

推荐答案

您正在将 String 添加到参数化的 List 中以接受 Student s.

You are adding Strings to a List parametrized to take Students.

这当然不会编译.

• 在您的 Student 类中添加一个构造函数，并接受一个 String 参数(以及其中的相关逻辑).
• 然后，使用以下成语: students.add(new Student("Student 1"));

• Add a constructor to your Student class, taking a String argument (and the relevant logic within).
• Then, use the following idiom: students.add(new Student("Student 1"));

要注意的是，泛型正是在那个阶段使编译失败.

To be noted, generics are there precisely to fail compilation at that stage.

如果您使用了原始的 List (Java 4样式)，则您的代码将已经编译，但是由于您希望 Student，在运行时会发生种种弊端对象包含在您的 List 中，但是您将得到 String s.

If you had used a raw List (Java 4-style), your code would have compiled, but all sorts of evil would have happened at runtime, since you'd expect Student objects to be contained in your List, but you'd get Strings instead.

这篇关于“在arraylist构造函数中找不到适用于add(java.lang.String)的合适方法"?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！