@Test public void testContainsElementToStringReturnsNull() { // 问题：如果 element.toString() 返回 null，会抛异常 assertThrows(NullPointerException.class ...

Even though we can explore the universe with great precision, there is still a lot we don't know, according to Ulf Danielsson, professor of theoretical physics at Uppsala University. Besides doing ...

Modify a String Instance Before we see how to modify a String we need to understand how the String object save its value. The String s were designed to be immutable, thus their values will not change.