public class NonNull {
    /**
     * Checks that the specified object reference is not {@code null}. This
     * method is designed primarily for doing parameter validation in methods
     * and constructors, as demonstrated below:
     * <pre>
     * public Foo(Bar bar) {
     *     this.bar = Objects.nonNull(bar);
     * }
     * </pre>
     *
     * @param obj the object reference to check for nullity
     * @return {@code obj} if not {@code null}
     * @throws NullPointerException if {@code obj} is {@code null}
     */
    public static <T> T nonNull(T obj) {
        if (obj == null)
            throw new NullPointerException();
        return obj;
    }

    /**
     * Checks that the specified object reference is not {@code null} and
     * throws a customized {@Link NullPointerException} if it is. This method
     * is designed primarily for doing parameter validation in methods and
     * constructors with multiple parameters, as demonstrated below:
     * <pre>
     * public Foo(Bar bar, Baz baz) {
     *     this.bar = Objects.nonNull(bar, "bar must not be null");
     *     this.baz = Objects.nonNull(baz, "baz must not be null");
     * }
     * </pre>
     *
     * @param obj     the object reference to check for nullity
     * @param message detail message to be used in the event that a {@code
     *                NullPointerException} is thrown
     * @return {@code obj} if not {@code null}
     * @throws NullPointerException if {@code obj} is {@code null}
     */
    public static <T> T nonNull(T obj, String message) {
        if (obj == null)
            throw new NullPointerException(message);
        return obj;
    }

    public static void main(String[] args) throws Exception {
        int errors = 0;
        errors += testNonNull();
        if (errors > 0)
            throw new RuntimeException();
    }

    private static int testNonNull() {
        int errors = 0;
        String s;

        // Test 1-arg variant
        try {
            s = nonNull("pants");
            if (s != "pants") {
                System.err.printf("1-arg non-null failed to return its arg");
                errors++;
            }
        } catch (NullPointerException e) {
            System.err.printf("1-arg nonNull threw unexpected NPE");
            errors++;
        }

        try {
            s = nonNull(null);
            System.err.printf("1-arg nonNull failed to throw NPE");
            errors++;
        } catch (NullPointerException e) {
            // Expected
        }

        // Test 2-arg variant
        try {
            s = nonNull("pants", "trousers");
            if (s != "pants") {
                System.err.printf("2-arg nonNull failed to return its arg");
                errors++;
            }
        } catch (NullPointerException e) {
            System.err.printf("2-arg nonNull threw unexpected NPE");
            errors++;
        }

        try {
            s = nonNull(null, "pantaloons");
            System.err.printf("2-arg nonNull failed to throw NPE");
            errors++;
        } catch (NullPointerException e) {
            if (e.getMessage() != "pantaloons") {
                System.err.printf("2-arg nonNull threw NPE w/ bad detail msg");
                errors++;
            }
        }
        return errors;
    }
}