Groovy example source code file (NullObjectTest.groovy)

This example Groovy source code file (NullObjectTest.groovy) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Java - Groovy tags/keywords

greeting, greeting, groovytestcase, groovytestcase, mycategory, mycategory, nullobjecttest, string, string

The Groovy NullObjectTest.groovy source code

package org.codehaus.groovy.runtime

class NullObjectTest extends GroovyTestCase {
    void testCallingMethod() {
        def foo = null
        shouldFail(NullPointerException) {
          println foo.bar
        }
    }
    
    void testtoStringMethod() {
        def foo = null
        assert foo.toString() == "null"
    }

    void testEquals() {
        def a = [1]
        assert a[3] == a[4]
        assert a[2].equals(a[4])
    }
    
    void testAsExpression() {
      assert null as String == null
    }
    
    void testIs(){
      assert null.is(null)
    }
    
    void testCategory() {
        def n = null

        assert "a $n b" == "a null b"
            assert n.toString() == "null"
            assert n + " is a null value" == "null is a null value"
            assert "this is a null value " + null == "this is a null value null"

            use (MyCategory) {
                assert "a $n b" == "a  b"
                assert n.toString() == ""
                assert n + " is a null value" == " is a null value"
                assert "this is a null value " + null == "this is a null value "
            }
        }

    void testClone() {
        def foo = null
        shouldFail(NullPointerException) {
            foo.clone()    
        }
    }
    
    void testEMC() {
        def oldMC = null.getMetaClass()
        NullObject.metaClass.hello = { -> "Greeting from null" }
        assert null.hello() == "Greeting from null"
        null.setMetaClass(oldMC)
    }
}

class MyCategory {
    public static String toString(NullObject obj) {
        return ""
    }
}