Question

Most classes need to be imported before they can be used in an application. Why is every application allowed to use classes System and String without first importing them?

Short answer

System and String are in the `java.lang` package, which is implicitly imported in every Java program.

Step-by-step solution

Understanding the Need for Importing Classes

In Java applications, we import classes from their respective packages to use them in our code. Packages are collections of related classes and interfaces. Importing helps in managing large codebases by organizing classes according to functionality.

Recognizing Special Packages - java.lang

The `java.lang` package is a core package in Java and provides fundamental classes that are extensively used in Java programming. This package contains essential classes such as `Object`, `System`, `String`, among others.

Identifying Java's Implicit Imports

Due to its importance, the `java.lang` package is implicitly imported by the Java compiler for every Java application. This means that any class from `java.lang`, such as `System` and `String`, can be accessed directly without an explicit import statement.

Applying the Concept to System and String Classes

Since `System` and `String` classes are part of the `java.lang` package, they are automatically available in any Java application. No import statement is needed because `java.lang` is implicitly imported by default.

Key concepts

java.lang package

The `java.lang` package is integral to Java programming. It contains core classes that Java programs frequently use, providing essential services that are foundational for app development. This package includes classes like `Object`, `String`, `System`, and many more. These classes are crucial because they provide the means to interact with standard Java functionalities such as input/output operations, threading, and basic data manipulation.
This package is so fundamental that it is implicitly loaded into every Java program by default. This means you don't have to manually import the `java.lang` package—it is always at your service. This feature of Java simplifies programming, as you do not need to worry about importing some of the most commonly used classes.

importing classes in Java

Importing classes in Java is akin to bringing pre-written code into your working file, allowing you to use code modules and features that are not inherently available in your program. This is done through `import` statements, written at the beginning of your Java file. For example, if you need to use a class from the `java.util` package, you would write:

• `import java.util.ClassName;`

Where `ClassName` is the class you wish to use. This process helps organize code, making it more modular.
Without importing necessary classes, Java programs would not be able to access the functions needed for specific operations, thus limiting their functionality and increasing the clutter of code as developers would need to rewrite existing implementations.

core Java classes

Core Java classes are the building blocks of Java applications. These classes are part of the Java library which provides the necessary tools to develop Java applications. They cover a wide array of functionalities, from handling basic data types to networking and database access.
Classes like `System`, `String`, and `Object` fall under core Java classes. They are derived from the `java.lang` package and, due to their importance, there is no need for developers to import these classes manually. This convenient feature streamlines Java programming.
Understanding core classes helps developers implement effective solutions with less code, as many built-in features and methods are already provided by Java. This significantly reduces the amount of new code needed and optimizes the development process.