instanceOf vs sameInstance

Question

I am programming a test class using Mockito. I have a class that has a method to return another class

public BuilderClass build(){
     return AnotherClass;
}

When I use

assertThat(BuilderClass.build(), is(instanceOf(AnotherClass.class)));

The test is ok but when I use

assertThat(BuilderClass.build(), is(sameInstance(AnotherClass.class)));

The test is wrong. So, What is the different between use instanceOf or sameInstance?

Regards.

A bit off-topic but please see: http://stackoverflow.com/questions/2790144/avoiding-instanceof-in-java When you use multiple instanceof in your code it can be considered as a "smell", the use of reflection can clean this up. — M. Suurland, May 18 '16 at 07:51
Thank you for off-topic. I didn't know about this situation. — Chema, May 18 '16 at 08:34

inigo skimmer · Accepted Answer · 2016-05-18T09:08:59.593

From javadoc

Creates a matcher that matches only when the examined object is the same instance as the specified target object.

Ie both pointers link to the same memory location.

Foo f1 = new Foo();
Foo f2 = f1;
assertThat(f2, is(sameInstance(f1)));

Here is the complete test:

public class FooTest {

class Foo {

}

private Foo f1 = new Foo();
private Foo f2 = new Foo();

/**
 * Simply checks that both f1/f2 are instances are of the same class
 */
@Test
public void isInstanceOf() throws Exception {
    assertThat(f1, is(instanceOf(Foo.class)));
    assertThat(f2, is(instanceOf(Foo.class)));
}

@Test
public void notSameInstance() throws Exception {
    assertThat(f2, not(sameInstance(f1)));
}

@Test
public void isSameInstance() throws Exception {
    Foo f3 = f1;
    assertThat(f3, is(sameInstance(f1)));
}
}

It'd be a better answer if you described what both do. – ChiefTwoPencils May 18 '16 at 07:54 — ChiefTwoPencils, May 18 '16 at 07:54

score 3 · Answer 2 · answered May 18 '16 at 07:53

3

sameInstance means that the two operands are references to the same memory location. instanceOf tests if the first operand is really an instance (object) of the second operand (class).

answered May 18 '16 at 07:53

AhmadWabbi

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instanceOf vs sameInstance

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