从Object获取ArrayList

Question

I have one method that returns an object with two arraylists:

return new Object[] {work, play};

I am trying to get them back out in another method. I have tried casting to ArrayList but I get the error 'array required, but java.lang.Object found'.

ArrayList setWork = (ArrayList)obj[0];
ArrayList setPlay = (ArrayList)obj[1];

Full code for ArrayList creation:

public static Object[] getWorkandPlay(ArrayList al) {

    ArrayList work = new ArrayList();
    ArrayList play = new ArrayList();

    for (int i=0; i<al.size(); i++){
        String item = (String) al.get(i);

        if (item.startsWith("w.")) {
            System.out.println("w " + item);
            work.add(item);
        } else if (item.startsWith("p.")) {
            System.out.println("p " + item);
            play.add(item);
        } else {
            System.out.println("Entries must start with either w. or p.\n");
        }
    }
    return new Object[] {work, play};
}

Answer 1

return new Object[] {work, play}; i think returns an array of object. Try ArrayList result = new ArrayList(); put work andd play inside result then return result. Then

Answer 2

In your calling code, you should set the reference type of obj as an Object array. You probably have Object obj = getWorkandPlay(anArrayList); in your code. Change it to Object[] obj = getWorkandPlay(anArrayList); .

Answer 3

I am doing something like this based on your code and it works...

class Test{
    public static Object[] getWorkandPlay(ArrayList al) {
        ArrayList work = new ArrayList();
        ArrayList play = new ArrayList();

        for (int i=0; i<al.size(); i++){
            String item = (String) al.get(i);

            if (item.startsWith("w.")) {
                System.out.println("w " + item);
                work.add(item);
            } else if (item.startsWith("p.")) {
                System.out.println("p " + item);
                play.add(item);
            } else {
                System.out.println("Entries must start with either w. or p.\n");
            }
        }
        return new Object[] {work, play};
    }
    public static void main(String[] args) {
        ArrayList<String> al=new ArrayList<>();
        al.add("w. test");
        al.add("p. test");
        Object[] obj=getWorkandPlay(al);
        ArrayList setWork = (ArrayList)obj[0];
        ArrayList setPlay = (ArrayList)obj[1];
    }
}

output

w w. test
p p. test

Answer 4

You probably have a typo somewhere in your code. This compiles for me:

import java.util.*;

public class SampleClass {

    public static void main(String[] args) {
        // Create an ArrayList and add some sample Strings
        ArrayList al = new ArrayList();
        al.add("w. test");
        al.add("p. test");

        Object[] obj = getWorkandPlay(al);

        ArrayList setWork = (ArrayList)obj[0];
        ArrayList setPlay = (ArrayList)obj[1];
    }

    public static Object[] getWorkandPlay(ArrayList al) {
        ArrayList work = new ArrayList();
        ArrayList play = new ArrayList();

        for (int i=0; i<al.size(); i++){
            String item = (String) al.get(i);

            if (item.startsWith("w.")) {
                System.out.println("w " + item);
                work.add(item);
            } else if (item.startsWith("p.")) {
                System.out.println("p " + item);
                play.add(item);
            } else {
                System.out.println("Entries must start with either w. or p.\n");
            }
        }

        return new Object[] {work, play};
    }
}