How to Statically Initialize Array Of Objects in Java

Question

How do I Statically initialize an array of objects in Java? A simple example of my intentions follows:

Say my object is

public class FRIEND {
    String name;
    String phone;
}

My intent is to do something like the below which doesn't work (I've tried variations with no luck).

static FRIEND[] MyFriends[] = {
    { "Bob",  "5551234" },
    { "Jack", "5716666" },
    { "Mary", "5341111" }
};

I'e found tons of examples of array initialization but they either (a) initialize arrays of primitives (e.g. int[]) or (b) use loops with explicit setting (e.g., MyFriends[n].name = "Bob");

What am I doing wrong?

Add a constructor to your class and put new FRIEND(...) in your array initialization. — khelwood
– khelwood, Commented Aug 23, 2019 at 14:43
I tried that but shouldn't it be "new FRIEND[]"? Also I am not sure about the syntax of the "..." in your suggestion. A more verbose example would be wonderful. — DontPanic
– DontPanic, Commented Aug 23, 2019 at 14:48

Butiri Dan · Accepted Answer · 2019-08-23 14:53:21Z

2

Create the FRIEND objects

static FRIEND[] MyFriends = {
        new FRIEND("Bob", "5551234"),
        new FRIEND("Jack", "5716666"),
        new FRIEND("Mary", "5341111")
};

Add a constructor to the FRIEND class

public class FRIEND {
    String name;
    String phone;

    public FRIEND(String name, String phone) {
        this.name = name;
        this.phone = phone;
    }
}

The full code (with java 8)

import java.util.Arrays;

class FRIEND {
    String name;
    String phone;

    static FRIEND[] MyFriends = {
            new FRIEND("Bob", "5551234"),
            new FRIEND("Jack", "5716666"),
            new FRIEND("Mary", "5341111")
    };

    public FRIEND(String name, String phone) {
        this.name = name;
        this.phone = phone;
    }

    @Override
    public String toString() {
        return "FRIEND{" +
                "name='" + name + '\'' +
                ", phone='" + phone + '\'' +
                '}';
    }

    public static void main(String[] args) {
        Arrays.stream(MyFriends).forEach(System.out::println);
    }

}

Output

FRIEND{name='Bob', phone='5551234'}
FRIEND{name='Jack', phone='5716666'}
FRIEND{name='Mary', phone='5341111'}

edited Aug 23, 2019 at 14:53

answered Aug 23, 2019 at 14:42

Butiri Dan

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1 Comment

DontPanic Over a year ago

worked perfectly! Thanks! Adding the constructor was the magic.

Marcos Echagüe · Accepted Answer · 2019-08-23 14:53:44Z

2

Maybe you can also use an enum like this:

public enum Friend
{
    BOB("Bob", "5551234"),
    JACK("Jack", "5716666"),
    MARY("Mary", "5341111");

    private String name;
    private String phone;

    Friend(String name, String phone) {
        this.name = name;
        this.phone = phone;
    }

    public String getName() {
        return name;
    }

    public String getPhone() {
        return phone;
    }
}

Is another option that can use.

Hope this can help you.

answered Aug 23, 2019 at 14:53

Marcos Echagüe

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Comments

dariosicily · Accepted Answer · 2019-08-29 15:17:37Z

2

As specified in Oracle code conventions "class names should be nouns, in mixed case with the first letter of each internal word capitalized", so instead of FRIEND better use Friend as your class name. Your static MyFriends array will be rewritten as

public static Friend[] MyFriends = {
            new Friend("Bob", "5551234"),
            new Friend("Jack", "5716666"),
            new Friend("Mary", "5341111")
}

Above the code of the Friend class:

package stackoverflow;

public class Friend {

    String name;
    String phone;

    public Friend(String name, String phone) {
        this.name = name;
        this.phone = phone;
    }

    @Override
    public String toString() {
        return "Friend [name=" + name + ", phone=" + phone + "]";
    }

    public static Friend[] MyFriends = {
            new Friend("Bob", "5551234"),
            new Friend("Jack", "5716666"),
            new Friend("Mary", "5341111")
    }

    public static void main(String[] args) {
        for (Friend friend : MyFriends) {
            System.out.println(friend);
        }
    }
}

edited Aug 29, 2019 at 15:17

answered Aug 23, 2019 at 15:18

dariosicily

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1 Comment

DontPanic Over a year ago

I agree. In general, I always use camel-case naming for code-bearing classes. I still prefer all-caps for "data-only" classes like the original FRIEND class in my question. Probably a hangover from 30+ years of C/C++ coding. Oh well, old-dog/old-tricks :)

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