How do I pass an array to a method?

Question

I have not been able to find a proper answer on any forums about this.
But how exactly do I pass an array to a class constructor?

public class TestArray {
   String name;
   String[] array;

   public TestArray(String name, String[] anArray){
          this.name = name;
          int len = anArray.length;
          this.array = new String[len];
          for (int i = 0; i < len; i++)
          {
              this.array[i] = new String(anArray[i]);
          }
   }

   public static void main(String[] args){
        String[] anArray = new String[2];
        anArray[0] = new String("Test");
        anArray[1] = new String("Test2");
        TestArray work = new TestArray("Jordan", anArray); // How to pass the array?
   }
}

@Joachim Sauer: Haha, we were editing this question at the same time... — Martijn Courteaux, Jun 01 '10 at 16:01

danben · Answer 1 · 2010-06-01T16:00:47.253

2

Your code will work, minus the question mark in the last line (edit - this was removed by the editor).

Your braces are also off - move the main function inside the class (you have one too many closing braces after the TestArray constructor).

Edit 2 - now that your question has been edited to fix your errors, it should work as expected. I am not sure if this is the best practice for SO, but that's a discussion for meta.

edited Jun 01 '10 at 16:00

answered Jun 01 '10 at 15:53

danben

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Wow this was exactly the problem. I had one to many braces and changing that one bracket made everything work. THANks! – ambidextorous Jun 01 '10 at 17:10

score 1 · Answer 2 · answered Jun 01 '10 at 16:03

public static void main(String[] args){
    String[] anArray = new String[2];
    anArray[0] = new String("Test");
    anArray[1] = new String("Test2");
    TestArray work = new TestArray("Jordan", anArray);
}

This will work perfectly, although there is a shorter way to initialize anArray:

public static void main(String[] args){
    String[] anArray = new String[] { "Test", "Test2" };
    TestArray work = new TestArray("Jordan", anArray);
}

Which in turn can be shortened to:

public static void main(String[] args){
    TestArray work = new TestArray("Jordan", new String[] { "Test", "Test2" });
}

By the way, String objects are immutable, so you don't have to initialize new strings every time. They can be used directly like this.

Last tip: Arrays.copyOf(anArray, anArray.length) also returns a copy of the array, without the the for-loop.

Thanks for the tip for copying the array. – ambidextorous Jun 01 '10 at 17:09 — ambidextorous, Jun 01 '10 at 17:09

Martijn Courteaux · Answer 3 · 2010-06-02T13:53:47.433

0

Exactly like you wrote...

Update:

Maybe you got a compiling error, if so, you placed a closing braces (}) too much in your code. I removed it by formatting your code. Maybe this was the problem...

edited Jun 02 '10 at 13:53

answered Jun 01 '10 at 15:54

Martijn Courteaux

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score 0 · Answer 4 · answered Jun 01 '10 at 15:54

0

Arrays are objects - so are passed them by reference. And you don't need to make copies yourself. If you really feel you have to copy then better use System.arraycopy.

answered Jun 01 '10 at 15:54

Anton

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'so are passed them by reference'. close, but not true: http://stackoverflow.com/questions/40480/is-java-pass-by-reference – Sean Patrick Floyd Jun 01 '10 at 15:58
your reasoning is otherwise correct, but technically a reference is passed by value – Sean Patrick Floyd Jun 01 '10 at 16:00
@seanizer: agree - java passes references by value :) – Anton Jun 01 '10 at 16:08

ShinTakezou · Answer 5 · 2010-06-01T16:08:59.637

What do you mean exactly? After you check the matching of {} (main must be into the class), and remove the ? after anArray, the program is compiled and work...: you passed the array correctly to the constructor... if you add

System.out.println(this.array[i]);

you will see your anArray content be printed as expected...

P.S. if your code was not for testing, but you wanted really to copy the array, use System.arraycopy like:

    this.array = new String[anArray.length];
    System.arraycopy(anArray, 0, this.array, 0, anArray.length-1);

See here for example.

Errata corrige it must be anArray.length and not anArray.length-1 since arraycopy wants the length, not the index as I remembered :)

How do I pass an array to a method?

5 Answers5

Update: