Java calling methods

Question

I have two classes in separate files and I'm trying to import one class from the other. I was wondering how I could go about doing that? The the test class is supposed to take both methods from the first class and display them. I was wondering how I would go about doing that?

The first class:

public class StringUtils {
    public static String padLeft(String orig, int n) {
        orig = "testing for lab06";
        return String.format("%1$-" + n + "orig", orig);
    }

    public static String padLeft(String orig, int n, char c) {
        return String.format("%1$-" + n + c + "orig", orig);
    }
}

The second (or test) class

public class StringUtilsTest {
    public static void main(String args[]) {
        System.out.println(padLeft);
        System.out.println(padLeft);
    }
}

If they're in the same package, you should be able to call them as StringUtils.padLeft(orig,n) and StringUtils.padLeft(orig,n,c) in StringUtilsTest — turbo
– turbo, Commented Feb 10, 2014 at 16:57
Well, assuming he has corresponding variables named orig, n, and c of the correct types in main(). — Dennis Meng
– Dennis Meng, Commented Feb 10, 2014 at 16:58
@DennisMeng Just put those as place holders since they are the parameter names — turbo
– turbo, Commented Feb 10, 2014 at 16:59

Nick Holt · Accepted Answer · 2014-02-10 17:19:01Z

1

Assuming both classes are in the same package (it looks like they're in the default package from the code in the question) you've got a couple of options.

The first option is to explicitly refer to the class containing the padLeft method like this:

public class StringUtilsTest
{
  public static void main(String args[])
  {
    System.out.println(StringUtils.padLeft("test 1", 5));
    System.out.println(StringUtils.padLeft("test 2", 5));
  }
}

Had StringUtils and StringUtilsTest been in different packages (not that usual for a class and its test) you would have needed to import StringUtils into StringUtilsTest with a normal import.

The second option is to use a import static like this:

import static StringUtils.padLeft;

public class StringUtilsTest
{
  public static void main(String args[])
  {
    System.out.println(padLeft("test 1", 5));
    System.out.println(padLeft("test 2", 5));
  }
}

edited Feb 10, 2014 at 17:19

answered Feb 10, 2014 at 17:01

Nick Holt

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2 Comments

JoaoFilipeClementeMartins Over a year ago

This will probably work but is not a good way for a beginner to do it. At least until he understands how constructor in java works and the creation of objects of a certain type.

Nick Holt Over a year ago

@JoaoFilipeClementeMartins the example looks as though it's using a utils class, which aren't commonly instantiated plus the methods on it are static make instantiation of a StringUtils pointless

JoaoFilipeClementeMartins · Accepted Answer · 2014-02-10 17:02:40Z

In java the main method is the one that is going to run the rest of the code. So what u need to do is inside the main create an object of type StringUtils:

public class StringUtilsTest{

public static void main(String[] args){
    StringUtils str = new StringUtils();
    System.out.println(str.padLeft("random string",5));
    System.out.println(str.padLeft("random string",5,"c"));
}

that str object now can hold the calls to the methods inside StringUtils class. For the methods to work properly you need to pass the arguments inside them like i did.

Note: Like this you are using the default constructor for java classes if you want to define the constructor you have to do in the class StringUtils the following:

public class StringUtils{
    public StringUtils(){
        //and in here set the behavior you wish it to have.
    }
}

Hope it helps

the methods are static, declaring the object is not necessary
but provides a good understanding about how java is object oriented and it also works with non static methods
user3199687 did not say (s)he wanted to understand OOP. While your code is correct, it uses more memory to store str, uses more processing to create str, is slower to type, and is generally bad practice.

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