Agile Javaв„ў: Crafting Code with Test-Driven Development

The String class is also part of the system class library. It belongs to the package named java.lang. So why haven't you had to either use its fully qualified class name (java.lang.String) or provide an import statement?

The Java library contains classes so fundamental to Java programming that they are needed in many, if not all, classes. The classes String and Object are two such classes. The ubiquitous nature of these classes is such that the designers of Java wanted to save you from the nuisance of having to specify an import statement for them everywhere.

If you refer to the String class, then the statement:

import java.lang.String;

is implicit in each and every Java source file.

When you learn about inheritance (Lesson 6), you will find that every class implicitly extends from the class java.lang.Object. In other words, if a class declaration does not contain an extends keyword, it is as if you coded:

class ClassName extends java.lang.Object

This is another shortcut provided by the Java compiler.