Kotlin中ArrayList存储tasks类对象报错及任务打印方法咨询

Let's break down what's going wrong and how to fix it, step by step.

Why Your Code Is Throwing an Error #

You're hitting two key issues here:

• Invalid ArrayList Initialization: The ArrayList constructor doesn’t accept individual objects as direct arguments. Valid constructors are either empty, take an initial capacity integer, or a single Collection (like a List). Passing two tasks instances directly isn’t allowed—there’s no overload for that.
• (Best Practice) Class Naming: In Kotlin, class names should start with an uppercase letter (so tasks → Task). This isn’t a hard error, but it’s a standard convention that makes your code easier to read and maintain.

Corrected Code #

First, let’s fix the Task class (with a proper name and a toString() override to make printing meaningful):

class Task(var title: String, var time: String) {
    // Override toString() to get a human-readable output when printing tasks
    override fun toString(): String {
        return "Task: '$title' (scheduled at $time)"
    }
}

Next, initialize your task list correctly. You have two simple options:

Option 1: Use mutableListOf() (Recommended) #

mutableListOf() creates a MutableList (implemented as an ArrayList under the hood on the JVM) and lets you pass elements directly:

fun main(args: Array<String>) {
    val tasksList = mutableListOf(
        Task("hello", "3am"),
        Task("meet amy", "5pm")
    )
}

Option 2: Use ArrayList with a Collection #

If you specifically need an ArrayList type, pass a List of tasks to the ArrayList constructor:

fun main(args: Array<String>) {
    val tasksList = ArrayList<Task>(
        listOf(
            Task("hello", "3am"),
            Task("meet amy", "5pm")
        )
    )
}

How to Print Your Tasks #

Now that your list is set up correctly, printing the tasks is straightforward. Since we overridden toString(), each task will print with its title and time instead of a generic object reference.

Loop Through the List #

Use a for loop to iterate and print each task:

for (task in tasksList) {
    println(task)
}

Or Use forEach #

A more concise way with Kotlin’s lambda syntax:

tasksList.forEach { println(it) }

Either way, the output will look like this:

Task: 'hello' (scheduled at 3am)
Task: 'meet amy' (scheduled at 5pm)

内容的提问来源于stack exchange，提问作者Funris