What is the difference between assert object!=null and Assert.assertNotNull(object)?

What is the difference between following two blocks of code?

@Test  
public void getObjectTest() throws Exception {
    Object object;
    //Some code
    Assert.assertNotNull(object);
}

AND

@Test  
public void getObjectTest() throws Exception {
    Object object;
    //Some code
    assert object!=null;
}

I do understand that Assert.AssertNotNull is a function call from TestNG and assert is a key word of Java ( introduced in Java 1.4 ). Are there any other differences in these two ? e.g. working, performance etc