Java: Verify Class Exists

Question

I thought this would be a trivial matter, but I can't seem to find a method similar to class_exists in Java. I'm writing a test to verify that a class name is defined. How can I replicate this in Java with jUnit?

<?php

$this->assertTrue(class_exists('Car'), 'Should have a class called "Car"');

TestCar.java

import org.junit.Assert;

import org.junit.Test;

public class TestCar {

    @Test
    public void testCarExists() {
            try {
                Class.forName("Car");
            } catch(ClassNotFoundException e) {
                Assert.fail("Should create a class called 'Car'.");
            }
     }
}

Car.java

public class Car {
    // just enough :-)
}

See if this helps: http://stackoverflow.com/questions/5794227/how-to-check-if-class-exists-somewhere-in-package — Hugo Sousa, Jan 30 '14 at 17:27
A possible reason that the above code may seem to fail (even though it should work) is that classForName requires the *entire* package-qualified name of the class. — Hot Licks, Jan 30 '14 at 19:52
Another possible reason for failure is that the class being referenced is not in the classpath for the current class loader. — Hot Licks, Jan 30 '14 at 19:53
I've had trouble trying to determine what the full path would be. Both files are located in the default package. @HotLicks — theGrayFox, Jan 30 '14 at 19:56
That's the thing, I don't know what name the default package is. @HotLicks — theGrayFox, Jan 30 '14 at 20:00

Mureinik · Accepted Answer · 2016-11-24T03:55:40.607

5

One advantage of Java is that you have a compiler, so usually this is a non-issue. If you compile your code properly and then, for some reason, drop a required jar file from the runtime environment, you'll get a java.lang.ClassNotFoundException, so that should be enough.

If you want to be super-extra-safe, you could try calling Class.forName:

@Test
public void testClassExists {
    try {
        Class.forName("org.mypackage.Car");
    } catch (ClassNotFoundException e) {
        Assert.fail("should have a class called Car");
    }
}

edited Nov 24 '16 at 03:55

answered Jan 30 '14 at 17:31

Mureinik

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This gives me a good enough idea to implement something similar. I appreciate the help! – theGrayFox Jan 30 '14 at 17:34
Quick question, if my class is specified in a default package, what would the file path be? I've been trying to figure this out for awhile now. I've specified ```Class.forName("Car");``` but this test is still failing and not finding the class. – theGrayFox Jan 30 '14 at 19:12
`Class.forName("Car")` should work just fine. Can you edit your original post (or better yet - open a new question) with the full stacktrace and class definition? – Mureinik Jan 30 '14 at 19:19
I've edited it. Note, both files are located in the default package. I can't see why jUnit giving me an initialization error when I've defined the class. – theGrayFox Jan 30 '14 at 19:33

Java: Verify Class Exists

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