001    /*  Copyright (c) 2000-2010 hamcrest.org
002     */
003    package org.hamcrest.core;
004    
005    import static org.hamcrest.core.IsNot.not;
006    import org.hamcrest.Description;
007    import org.hamcrest.Matcher;
008    import org.hamcrest.Factory;
009    import org.hamcrest.BaseMatcher;
010    
011    /**
012     * Is the value null?
013     */
014    public class IsNull<T> extends BaseMatcher<T> {
015        @Override
016        public boolean matches(Object o) {
017            return o == null;
018        }
019    
020        @Override
021        public void describeTo(Description description) {
022            description.appendText("null");
023        }
024    
025        /**
026         * Creates a matcher that matches if examined object is <code>null</code>.
027         * <p/>
028         * For example:
029         * <pre>assertThat(cheese, is(nullValue())</pre>
030         * 
031         */
032        @Factory
033        public static Matcher<Object> nullValue() {
034            return new IsNull<Object>();
035        }
036    
037        /**
038         * A shortcut to the frequently used <code>not(nullValue())</code>.
039         * <p/>
040         * For example:
041         * <pre>assertThat(cheese, is(notNullValue()))</pre>
042         * instead of:
043         * <pre>assertThat(cheese, is(not(nullValue())))</pre>
044         * 
045         */
046        @Factory
047        public static Matcher<Object> notNullValue() {
048            return not(nullValue());
049        }
050    
051        /**
052         * Creates a matcher that matches if examined object is <code>null</code>. Accepts a
053         * single dummy argument to facilitate type inference.
054         * <p/>
055         * For example:
056         * <pre>assertThat(cheese, is(nullValue(Cheese.class))</pre>
057         * 
058         * @param type
059         *     dummy parameter used to infer the generic type of the returned matcher
060         */
061        @Factory
062        public static <T> Matcher<T> nullValue(Class<T> type) {
063            return new IsNull<T>();
064        }
065    
066        /**
067         * A shortcut to the frequently used <code>not(nullValue(X.class)). Accepts a
068         * single dummy argument to facilitate type inference.</code>.
069         * <p/>
070         * For example:
071         * <pre>assertThat(cheese, is(notNullValue(X.class)))</pre>
072         * instead of:
073         * <pre>assertThat(cheese, is(not(nullValue(X.class))))</pre>
074         * 
075         * @param type
076         *     dummy parameter used to infer the generic type of the returned matcher
077         *  
078         */
079        @Factory
080        public static <T> Matcher<T> notNullValue(Class<T> type) {
081            return not(nullValue(type));
082        }
083    }
084