Java Static用法及代碼示例

// Java program to Demonstrate How to
// Implement Static and Non-static Classes
// Class 1
// Helper class
class OuterClass {
    // Input string
    private static String msg = "GeeksForGeeks";
    // Static nested class
    public static class NestedStaticClass {
        // Only static members of Outer class
        // is directly accessible in nested
        // static class
        public void printMessage()
        {
            // Try making 'message' a non-static
            // variable, there will be compiler error
            System.out.println(
                "Message from nested static class: " + msg);
        }
    }
    // Non-static nested class -
    // also called Inner class
    public class InnerClass {
        // Both static and non-static members
        // of Outer class are accessible in
        // this Inner class
        public void display()
        {
            // Print statement whenever this method is
            // called
            System.out.println(
                "Message from non-static nested class: "
                + msg);
        }
    }
}
// Class 2
// Main class
class GFG {
    // Main driver method
    public static void main(String args[])
    {
        // Creating instance of nested Static class
        // inside main() method
        OuterClass.NestedStaticClass printer
            = new OuterClass.NestedStaticClass();
        // Calling non-static method of nested
        // static class
        printer.printMessage();
        // Note: In order to create instance of Inner class
        //  we need an Outer class instance
        // Creating Outer class instance for creating
        // non-static nested class
        OuterClass outer = new OuterClass();
        OuterClass.InnerClass inner
            = outer.new InnerClass();
        // Calling non-static method of Inner class
        inner.display();
        // We can also combine above steps in one
        // step to create instance of Inner class
        OuterClass.InnerClass innerObject
            = new OuterClass().new InnerClass();
        // Similarly calling inner class defined method
        innerObject.display();
    }
}