Java: Adding a class function in the main class

Question

I am new to JAVA. I want to create a class and write a function in it. I then want to use that function in the main class.

import java.util.Scanner;

public class multi_fun {
    public static void main(String[] args) {

        Scanner scan = new Scanner(System.in);
        int a, b, c;

        System.out.println("Enter 1st number: ");
        a = scan.nextInt();
        System.out.println("Enter 2nd number: ");
        b = scan.nextInt();
        Addition obj = new Addition();
        c = obj.add(a,b);
        System.out.println("The sum is "+c);
        scan.close();
    }
}
class Addition{
    public int add (int a, int b)
    {
        return(a+b);
    }
}

I am getting an error message, The type Addition is already defined. — Vikram Sharma, May 25 '17 at 10:04
you are doing a good think, your code work fine, what is your problem then? — YCF_L, May 25 '17 at 10:05
Try to clean Eclipse if you are using it. Your code is working fine — Alberto Pérez, May 25 '17 at 10:06
Here is the error message: Exception in thread "main" java.lang.NoSuchMethodError: Addition.add(II)I at multi_fun.main(multi_fun.java:15) — Vikram Sharma, May 25 '17 at 10:07
Can you post your whole source code tree? It seems to be problem with your source files, not the code. — Michał Piątkowski, May 25 '17 at 10:10
Error: The type Addition is already defined. Illegal modifier for the class Addition, only abstract, & final are permitted. — Vikram Sharma, May 25 '17 at 10:13
Please edit your question with the full stack trace error you are ceveiving, what are you doing and such. It's difficult to follow what you are doing just reading the comments. — Averroes, May 25 '17 at 10:16
A class which is not nested within another class typically goes in its own source file. Could having `Addition` and `multi_fun` in the same source file be an issue here? — Kevin Anderson, May 25 '17 at 10:19
@VikramSharma without proper description we cannot answer. So add error message(not as a comment). — Blasanka, May 25 '17 at 10:19
@KevinAnderson No it is not a problem here. I've tried it also — Blasanka, May 25 '17 at 10:21
@Blasanka: All the error message are listed in the comment sections. — Vikram Sharma, May 25 '17 at 10:22
And also what is the editor you are using? add it to the question also. No one cannot go through the comments and answer. You have to improve your question. — Blasanka, May 25 '17 at 10:29

score 1 · Answer 1 · answered May 25 '17 at 10:25

1

Make sure both the java files are in the same folder.

MultiFun.java

import java.util.Scanner;

public class MultiFun {

    public static void main(String[] args) {
        Addition obj = new Addition();

        Scanner scan = new Scanner(System.in);
        int a, b, c;

        System.out.println("Enter 1st number: ");
        a = scan.nextInt();
        System.out.println("Enter 2nd number: ");
        b = scan.nextInt();

        c = obj.add(a, b);
        System.out.println("The sum is " + c);
        scan.close();

    }

}

Addition.java

class Addition {
    public int add(int a, int b) {
        return (a + b);
    }
}

run the following commands

javac MultiFun.java
java MultiFun

answered May 25 '17 at 10:25

Anto Antony

792
3
11

His two classes in the same file. – Blasanka May 25 '17 at 10:27
do not need to create two java file using one java file this can be done. – Blasanka May 25 '17 at 13:03
Yeah.. we can do it in both way. – Anto Antony May 25 '17 at 13:07

Oghli · Accepted Answer · 2017-05-25T12:18:26.893

1

The problem I think according to error message you mentioned in the comments:

Exception in thread "main" java.lang.NoSuchMethodError: Addition.add(II)I at multi_fun.main(multi_fun.java:15)

It seems that you are putting class Addition declaration in the same source file of multi_fun.java program.

You should create a java class file called Addition.java and put your class code in it:

class Addition{
    public int add (int a, int b)
    {
        return(a+b);
    }
}

After that it should work without any errors.

Update:

You can check this Answer which explain Causes of 'java.lang.NoSuchMethodError: main Exception in thread “main”'it would be a useful solution to your problem.

edited May 25 '17 at 12:18

answered May 25 '17 at 11:34

Oghli

1,585
1
9
29

Do not need to create to Addition.java file in the same class can have multiple class. But make sure all classes are not `public`. And only run main class. – Blasanka May 25 '17 at 13:02
1

Yes he can do it in that way. but it's better to separate classes file from the main java program file. he should know the good practices to write java program in clean and organized way. also I update my answer and put link to the reasons of this error and the suggested solutions to it. – Oghli May 25 '17 at 14:47

Blasanka · Answer 3 · 2017-05-27T07:58:05.303

0

If you are run your program using Terminal or command prompt(cmd) make sure to run the class that have main method(created object from Addition class). And also do not create main methods in both classes and do not add public to Addition class.

One last thing: compile and run only the main class(multi_fun). Which is,

javac multi_fun.java
java multi_fun

edited May 27 '17 at 07:58

answered May 25 '17 at 10:26

Blasanka

14,208
6
76
90

score 0 · Answer 4 · answered May 25 '17 at 10:27

import java.util.Scanner;

public class multi_fun {

    public static void main(String[] args) {

        Scanner scan = new Scanner(System.in);
        int a, b, c;

        System.out.println("Enter 1st number: ");
        a = scan.nextInt();
        System.out.println("Enter 2nd number: ");
        b = scan.nextInt();
        add(a,b);
        System.out.println("The sum is "+c);
        scan.close();

    }

}


public static int add (int a, int b)
{
    return(a+b);
}

score 0 · Answer 5 · answered May 26 '17 at 06:47

The reason for this error is that there was already an other file in the same folder named Addition. So when I wrote a Class with the same name and tried to create an object, it was giving error message, as the parameters where different.

Thank you everyone for your help.

Java: Adding a class function in the main class

5 Answers5