Java NoSuchMethodError: main

Question

I am learning Java on OS X through terminal. When I compile the code below I do not get any errors but When I try to run it I get

Exception in thread "main" java.lang.NoSuchMethodError: main

My code:

public class Problem5{
public void main(String[] args) {
    int n = 1;
    while(!checkMod(n)){
        n++;
    }

}
public boolean checkMod(int in)
{
    int count = 0;
    for(int i=1; i<20; i++)
    {
        if(in%i == 0)
        {
            count = count + 1; 
        }
    }
    if(count ==19)
    {
        return true;
    }
    else{
        return false;
    }
}
}

I removed "static" from the main method because I am calling the checkMod method.

How do I code this correctly?

Thanks

mac:Java name$ javac Problem5.java mac:Java name$ java Problem5 — stackErr, Aug 16 '12 at 05:59
declare main method as static and call checkmod method with object as u cant call non-static method from static method.. — Sandeep Kumar, Aug 16 '12 at 06:00

score 5 · Accepted Answer · answered Aug 16 '12 at 06:01

5

Every executable Java program requires at least one class that implements public static void main(String args[]) in order to run.

Rather then removing the static reference from main, either

Add static to the public boolean checkMod(int in) ie public static boolean checkMod(int in)

or

Call the method checkMod from the instance level.

public class Problem5{
    public void main(String[] args) {
        new Problem5();
    }

    public Problem5() {
        int n = 1;
        while(!checkMod(n)){
            n++;
        }

    }

    // Rest of code...
}

answered Aug 16 '12 at 06:01

MadProgrammer

323,026
21
204
329

thanks for the info! This really helps. When would you want to create an instance vs having several static methods? – stackErr Aug 16 '12 at 06:05
1

`static` references are really good for utilities methods, things that don't require a reference to any instance objects, methods or variables. You want to use instances when you want more then one, well, instance of the object, such as `Person`. You program would be pretty useless if the `Person` class only used `static` references, you'd only ever be able to have one `Person`, BUT, you could use a `static` method to calculate the age, based a `Person`'s date of birth – MadProgrammer Aug 16 '12 at 06:10

score 1 · Answer 2 · answered Aug 16 '12 at 05:59

1

main need to be static: public static void main(String[] args)

answered Aug 16 '12 at 05:59

score 1 · Answer 3 · answered Aug 16 '12 at 06:00

1

The "entry-point" method is static main instead of main. They have different method signature. JVM will only search for static main. You can make your

public boolean checkMod(int in)

as

static public boolean checkMod(int in)

answered Aug 16 '12 at 06:00

user1192878

684
1
7
19

score 1 · Answer 4 · answered Aug 16 '12 at 06:02

static is required for the main method. You can use something like this to add state to your main execution:

public class Problem5 {
  public static void main(String[] args) {
    new Problem5().start();
  }

  private void start() {
    int n = 1;
    while(!checkMod(n)){
      n++;
    }
  }

  private boolean checkMod(int in) {
    ..
  }
}

On the other hand, your checkMod(int) method doesn't need state. You could also just add the static keyword to it as well. It can then be called by the static main method.

score 0 · Answer 5 · answered Aug 16 '12 at 05:59

0

You need to declare 'static' on both main and checkMod.

answered Aug 16 '12 at 05:59

Gary S.

394
2
7

score 0 · Answer 6 · answered Aug 16 '12 at 06:01

You need to make checkMod static as well, because you're calling it from another static method. You cannot call an instance method from a static method:

public class Problem5{
public static void main(String[] args) {
    int n = 1;
    while(!checkMod(n)){
        n++;
    }

}
public static boolean checkMod(int in)
{
    int count = 0;
    for(int i=1; i<20; i++)
    {
        if(in%i == 0)
        {
            count = count + 1; 
        }
    }
    if(count ==19)
    {
        return true;
    }
    else{
        return false;
    }
}
}

Sandeep Kumar · Answer 7 · 2012-08-16T06:09:20.897

Main method should always be declared as static. Also you are accessing checkMod in main method so either declare checkMod also as static or access it with object as you can not access non-static method from static method.

Try following.

public class Problem5{
public static void main(String[] args) {
    int n = 1;
    while(!new Problem5().checkMod(n)){
        n++;
    }

}
public boolean checkMod(int in)
{
    int count = 0;
    for(int i=1; i<20; i++)
    {
        if(in%i == 0)
        {
            count = count + 1;
        }
    }
    if(count ==19)
    {
        return true;
    }
    else{
        return false;
    }
}
}

Java NoSuchMethodError: main

7 Answers7