Description Casper Færgemand 2017-08-01 16:16:27 EDT

One of the following JUnit tests fail:

	class A {
		boolean called = false;

		void callOnce(int i) {
			if (called) {
				throw new IllegalArgumentException();
			} else {
				called = true;
			}
		}
	}

	@Test
	public void fine() {
		IntStream.of(1, 2, 3).forEach(i -> new A().callOnce(i));
	}

	@Test
	public void error() {
		IntStream.of(1, 2, 3).forEach(new A()::callOnce);
	}

Fine and error can be changed to one another using Ctrl + 1 and Convert to lambda expression or Convert to method reference, but the semantics of the two are not identical. Fine creates a new A for each forEach, while error reuses the same instance of A for each forEach.