What does inner mean in java

In Java, the "inner" keyword is used to create an inner class defined in another class, including nested classes, static nested classes, and inner classes. Nested classes and static nested classes can access all non-private members of the outer class, while inner classes can only access non-private members of the outer class. Inner classes are often used to organize functional code into logical groups and improve the maintainability and readability of the code.

Inner meaning in Java

In the Java programming language, the "inner" keyword is used to create Inner class. An inner class is a class defined in another class, called an outer class.

Types of inner classes

There are three types of inner classes in Java:

• Nested class : Defined in the non-static method of the external class.
• Static Nested class: Defined in the static method of the external class.
• Inner class: Defined in the instance method of the external class.

Access permissions of inner classes

• Nested classes and static nested classes can access all members of the outer class (except private members).
• Inner classes can only access non-private members of outer classes.

Purpose of inner classes

Inner classes are typically used to organize functional code into logical groups. They can also access private members of external classes, thereby improving code maintainability and readability.

Example

// 外部类
public class OuterClass {

    private int number;

    // 嵌套类
    public class NestedClass {

        public void printNumber() {
            System.out.println(number);
        }
    }

    // 静态嵌套类
    public static class StaticNestedClass {

        public static void printMessage() {
            System.out.println("Static nested class message");
        }
    }

    // 内部类
    public InnerClass getInnerClass() {
        // 内部类定义在实例方法中
        class InnerClass {

            public void printName() {
                System.out.println("Inner class name");
            }
        }

        return new InnerClass();
    }

    // 主函数
    public static void main(String[] args) {
        OuterClass outerClass = new OuterClass();
        NestedClass nestedClass = outerClass.new NestedClass();
        nestedClass.printNumber();

        StaticNestedClass.printMessage();

        InnerClass innerClass = outerClass.getInnerClass();
        innerClass.printName();
    }
}

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