java 使用 ArrayList 作为构造函数的参数

Using an ArrayList as Parameter of Constructor

提问by James Scholes

I'm trying to write a constructor for a class which accepts an ArrayList (containing integers) as one of it's arguments. When instantiating this class later, I will pass an appropriate, pre-populated list of values, so I don't want to create an empty list inside the constructor.

我正在尝试为一个类编写一个构造函数，该类接受一个 ArrayList（包含整数）作为它的参数之一。稍后实例化此类时，我将传递一个适当的、预先填充的值列表，因此我不想在构造函数中创建一个空列表。

Unfortunately, when I try to compile the below code, Java spits out five errors, all related to line 23 (my constructor's function definition). Any advice would be appreciated:

不幸的是，当我尝试编译下面的代码时，Java 吐出五个错误，都与第 23 行（我的构造函数的函数定义）有关。任何意见，将不胜感激：

/*
 * SumGenerator
 * 
 * @author James Scholes
*/

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

public class SumGenerator
{
    // Some initial variables
    public int timesTable;
    public int multiple;

    /*
     * Constructor
     * 
     * @param timesTable(int): The times table to use for sum generation
     * @param limit(int): The highest multiple to use in sum generation
     * @param previousMultiples(ArrayList<Integer>): The previously used multiples to avoid sum duplication
    */
    public SumGenerator(int timesTable, int limit = 10, ArrayList<Integer> previousMultiples)
    {
        this.timesTable = timesTable;
        Random randomGenerator = new Random();

        // Create a list to store our multiples
        ArrayList<Integer> multiples = new ArrayList<Integer>();
        // and add our multiples to it, only if 
        // they haven't been used before
        for(int i = timesTable; i <= limit; i++)
        {
            if(previousMultiples.contains(i))
            {
                continue;
            }
            else
            {
                multiples.add(i);
            }
        }

        this.multiple = multiples.get(randomGenerator.nextInt(multiples.size()));
    }

}

SumGenerator.java:23: error: ')' expected
    public SumGenerator(int timesTable, int limit = 10, ArrayList<Integer> previousMultiples)
                                                 ^
SumGenerator.java:23: error: illegal start of type
    public SumGenerator(int timesTable, int limit = 10, ArrayList<Integer> previousMultiples)
                                                    ^
SumGenerator.java:23: error: <identifier> expected
    public SumGenerator(int timesTable, int limit = 10, ArrayList<Integer> previousMultiples)
                                                      ^
SumGenerator.java:23: error: ';' expected
    public SumGenerator(int timesTable, int limit = 10, ArrayList<Integer> previousMultiples)
                                                       ^
SumGenerator.java:23: error: <identifier> expected
    public SumGenerator(int timesTable, int limit = 10, ArrayList<Integer> previousMultiples)
                                                                                            ^
5 errors

回答by djechlin

Java doesn't support default arguments.

Java 不支持默认参数。

回答by rgettman

You can't supply default values for parameters in Java: int limit = 10. To work around, supply overloaded constructors. One doesn't have limitand will supply the other with the default value.

您不能为 Java 中的参数提供默认值：int limit = 10. 要解决此问题，请提供重载的构造函数。一个没有limit并且将为另一个提供默认值。

public SumGenerator(int timesTable, ArrayList<Integer> previousMultiples)
{
    this(timesTable, 10, previousMultiples);
}

public SumGenerator(int timesTable, int limit, ArrayList<Integer> previousMultiples)
{
    // Your constructor here.
}

回答by Jesper

public SumGenerator(int timesTable, int limit = 10, ArrayList<Integer> previousMultiples)

Remove the = 10in int limit = 10. Java does not support default values for constructor or method arguments.

删除= 10在int limit = 10. Java 不支持构造函数或方法参数的默认值。