Simple Java array question

Question

Why does this work while the other throws errors:

import java.util.*;

//This works fine
public class ArrayTest {
    public static String[] names = {"James", "John", "Mark"};
    public static void main( String args[] ){
        System.out.print("Names: " + Arrays.toString(names));
    }
}

//But why does this not?
public class ArrayTest {
    public static String[] names = new String[3];
    names[0] = "James";
    names[1] = "John";
    names[2] = "Mark";
    public static void main( String args[] ){
        System.out.print("Names: " + Arrays.toString(names));
    }
}

try putting names[0] = "James"; names[1] = "John"; names[2] = "Mark"; inside main. — ColWhi
– ColWhi, Commented Apr 19, 2011 at 12:40
Try putting the names[number] pieces in a static {} block. — josh.trow
– josh.trow, Commented Apr 19, 2011 at 12:40
You can't have arbitrary statements outside of a method/constructor/initializer. — Joachim Sauer
– Joachim Sauer, Commented Apr 19, 2011 at 12:41

Stephen C · Accepted Answer · 2011-04-19 12:46:21Z

4

Try it like this:

public class ArrayTest {
    public static String[] names;

    static
    {
        names = new String[3];
        names[0] = "James";
        names[1] = "John";
        names[2] = "Mark";
    }

    public static void main( String args[] ){
        System.out.print("Names: " + Arrays.toString(names));
    }
}

edited Apr 19, 2011 at 12:46

Stephen C

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answered Apr 19, 2011 at 12:40

duffymo

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1 Comment

duffymo Over a year ago

Thank you for the correction, Stephen C. Greatly appreciated.

Jan Zyka · Accepted Answer · 2011-04-19 12:41:30Z

1

Enclose the array init inside static init block like follows:

static {
 names[0] = "James";     
 names[1] = "John";     
 names[2] = "Mark"; 
}

answered Apr 19, 2011 at 12:41

Jan Zyka

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1 Comment

enchance Over a year ago

I didn't know you could do that.

janhink · Accepted Answer · 2011-04-19 12:42:40Z

You cannot assign values to the array in the class declaration. You have to do it in a body of a method, e.g. the main method.

public class ArrayTest {

    public static String[] names = new String[3];

    public static void main( String args[] ) {
        names[0] = "James";
        names[1] = "John";
        names[2] = "Mark";
        System.out.print("Names: " + Arrays.toString(names));
    }
}

Or do it in a static block like this:

public class ArrayTest {

    public static String[] names = new String[3];

    static {
        names[0] = "James";
        names[1] = "John";
        names[2] = "Mark";
    }

    public static void main( String args[] ) {        
        System.out.print("Names: " + Arrays.toString(names));
    }
}

Dakshinamurthy Karra · Accepted Answer · 2011-04-19 12:40:27Z

0

Put the initialization in a static block. Else it is run only when a object of that type is instantiated.

answered Apr 19, 2011 at 12:40

Dakshinamurthy Karra

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Comments

Michael Borgwardt · Accepted Answer · 2011-04-19 12:44:06Z

0

The second is invalid syntax. A class declaration can contain only field definitions, method definitions, nested class definitions, and initializer blocks, but not plain statements like names[0] = "James";

Thus, you have to put those statements into a method (which can be called by a field initializer) or an initializer block.

answered Apr 19, 2011 at 12:44

Michael Borgwardt

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Comments

Peter Lawrey · Accepted Answer · 2011-04-19 12:49:59Z

0

A syntax I like is as follows (esp. for long lists)

public static final String[] names = "James,John,Mark".split(",");

answered Apr 19, 2011 at 12:49

Peter Lawrey

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Comments

Phil · Accepted Answer · 2011-04-19 13:04:28Z

0

The simple reason :

You cannot execute instructions in the declaration of the class, unless you use a static block such as :

static { names[0] = "James"; names[1] = "John"; names[2] = "Mark"; }

But be aware that a static block is executed once, when the class is loaded by the Java virtual machine.

Therefore, if you create several instances of your class, the static block will still only be executed once.

answered Apr 19, 2011 at 13:04

Phil

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