Why can only one class be declared as public in a Java file?

Multiple Classes in a Java File: Purpose and Restrictions

Java allows multiple classes to be defined within a single .java file. However, there are certain restrictions to consider.

Public Top-Level Classes

Within a .java file, only one class can be declared as a public top-level class. This class must have the same name as the source file. Any additional classes must be defined as nested (inner) classes within the public class.

Example:

<code class="java">// MyJavaFile.java
public class MyJavaFile {

    // Inner class
    class InnerClass {
        // Inner class methods and variables
    }

    // Public class methods and variables
}</code>

Purpose of Multiple Classes

Including multiple classes in a single file serves the purpose of bundling related functionality together. Nested classes can be used to represent support data structures, support classes, or other internal implementations that are closely tied to the functionality of the public class.

This practice aids in code readability by grouping related classes and reducing the number of separate source files. However, it is not mandatory to use multiple classes in a single file. The decision to do so is based on the specific design and organization needs of the code.

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