Junit explained in plain english please.

Question

I been reading up on JUnit, and i still do not understand it.
What is the difference? Why not just make an application?
Please explain it as if you are explaining it to someone who is not very technical.
Thank you

Answer 1

What is the difference? Why not just make an application?You could. But it wouldn't be as nice.
If you have 100 tests, how are you going to organise them in your application? Will you write 100 different applications?
JUnit allows you to group tests nicely.
It allows you to share setup/teardown logic to prepare for running your tests.
It gives you a nice graphical display of how tests went if you're using an IDE (or the command line).
If you're using a tool like ant, it allows you to stop the script when you encounter a failed test. That's really useful if you're building something based on libraries - you don't want to build the rest of the webapp if one of the libraries it will be made from has a bug in it.
No, you don't have to use JUnit, but it's much easier to use JUnit than it is not to.
The simple example you asked for. Here's a real test case that I'm using to check to see if a component for breaking down web URIs is working correctly. Note how I use the nice simple "assertion" methods.
public class PathHolderTest extends TestCase {
   public void testRootPathAbsolute() {
      final PathHolder ph = new PathHolder("/");
      assertTrue(ph.isFolderPath());
      assertTrue(ph.isAbsolutePath());
      assertEquals(1,ph.getPathElements().length);
      assertEquals("/",ph.getPathElements()[0]);
   public void testSimplePathAbsolute() {
      final PathHolder ph = new PathHolder("/foo");
      assertFalse(ph.isFolderPath());
      assertTrue(ph.isAbsolutePath());
      assertEquals(2,ph.getPathElements().length);
      assertEquals("/",ph.getPathElements()[0]);
      assertEquals("foo",ph.getPathElements()[1]);
   public void testFolderPathAbsolute() {
      final PathHolder ph = new PathHolder("/foo/");
      assertTrue(ph.isFolderPath());
      assertTrue(ph.isAbsolutePath());
      assertEquals(2,ph.getPathElements().length);
      assertEquals("/",ph.getPathElements()[0]);
      assertEquals("foo",ph.getPathElements()[1]);
   public void testSubFilePathAbsolute() {
      final PathHolder ph = new PathHolder("/foo/bar");
      assertFalse(ph.isFolderPath());
      assertTrue(ph.isAbsolutePath());
      assertEquals(3,ph.getPathElements().length);
      assertEquals("/",ph.getPathElements()[0]);
      assertEquals("foo",ph.getPathElements()[1]);
      assertEquals("bar",ph.getPathElements()[2]);
   public void testSubFilePathWithExtensionAbsolute() {
      final PathHolder ph = new PathHolder("/foo/bar/index.html");
      assertFalse(ph.isFolderPath());
      assertTrue(ph.isAbsolutePath());
      assertEquals(4,ph.getPathElements().length);
      assertEquals("/",ph.getPathElements()[0]);
      assertEquals("foo",ph.getPathElements()[1]);
      assertEquals("bar",ph.getPathElements()[2]);
      assertEquals("index.html",ph.getPathElements()[3]);
}