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package com.uc;
/**
* What's the nested class ?
* define a class within another class
* Why to use nested class ?
* <li>It is a way of logically grouping classes that are only used in one place.</li>
* <li>It increases encapsulation.</li>
* <li>Nested classes can lead to more readable and maintainable code.</li>
*
*
*/
public class NestClassT {
public static void main(String[] args) {
//test();
test1();
}
/**
* 测试instance nested class的用法
*/
private static void test1() {
// TODO Auto-generated method stub
Outer outerObj = new Outer();
Outer.InnerClass obj = outerObj.new InnerClass();
obj.showInfo(" Called by Create context");
//查看inner class 是否可修改value of enclosing class variable
System.out.println(outerObj.getInstanceVal());
}
/**
* 测试static nested class 与 static variable of enclosing class 的访问关系
*/
private static void test() {
// TODO Auto-generated method stub
Outer.StaticInner obj = new Outer.StaticInner();
//可以访问static variable of enclosing class
obj.showInfo();
//测试 static method of static nested class 对enclosing class的访问性
Outer.StaticInner.staticMethod();
//从上面的测试可以看出 static nested class 与 static method of enclosing class
//的访问性一致
//还有一点需要注意的是，the modifiers of static nested class
//{public, protected, private and packet private}
}
}
class Outer {
/**
* static nested class modifiers can be
* {public protected private and packet private}
*/
public static class StaticInner {
public void showInfo () {
//查看static nested class 是否可访问Enclosing class
//static variable
System.out.println(info + " in instance method of static nested class");
System.out.println(instanceVal + " in instance method of static nested class");
System.out.println(outerInfo);
//variable shadow
//我们可以通过完整的名称引用来解决命名冲突的问题
System.out.println(Outer.info);
//调用static private method of enclosing class
System.out.println("Call static private method of enclosing class: ");
System.out.println(staticMethodOfOuter(" called by instance method of static nested class call "));
}
public static void staticMethod() {
//访问外部变量，实际上是编译器在中间做了手脚，这个可以通过 javap命令查看
System.out.println(outerInfo);
System.out.println(info + " in static method of static nested class");
//variable shadow
//我们可以通过完整的名称引用来解决命名冲突的问题
System.out.println(Outer.info);
//calling static private method of enclosing class
System.out.println("Calling static private method of enclosing class: ");
System.out.println(staticMethodOfOuter(" called by static method of static nested class call "));
}
//the static variable of static nested class
private static String info = "static val";
//the instance variable of static nested class
private String instanceVal = "instanceVal";
}
//test the variable shadow
//there is a 'info' variable in the static nested class
private static String info = "private static info of enclosing class";
private static String outerInfo = "static val of enclosing class";
private static String staticMethodOfOuter(String val) {
return "I am static private method of enclosing class" + val;
}
//////////////////////////////////////////////////////////////////////
//下面测试instance nested class 对 enclosing class 的访问性
//
//As with instance methods and variables,
//an inner class is associated with an instance of its enclosing class
//and has direct access to that object's methods and fields.
//
//Also, because an inner class is associated with an instance,
//it cannot define any static members itself.
//
//To instantiate an inner class, you must first instantiate the outer class.
//Then, create the inner object within the outer object with this syntax:
// OuterClass.InnerClass innerObject = outerObject.new InnerClass();
//Additionally, there are two special kinds of inner classes:
//local classes and anonymous classes.
//////////////////////////////////////////////////////////////////////
private String instanceOuterInfo = "I am Instance variable of enclosing class";
private String instanceVal = "I am instance variable of enclosing method";
public String getInstanceVal() {
return this.instanceOuterInfo;
}
private String instanceMethod(String val) {
return "I am instance method of enclosing class " + val;
}
class InnerClass {
//The field info cannot be declared static in a non-static inner type,
//unless initialized with a constant expression
static final String info = "test";
private String instanceVal = "I am instance varaible of instance nested method";
/**
* The method staticMethod cannot be declared static;
* static methods can only be declared in a static or top level type
*/
// public static void staticMethod() {
//
// }
public void showInfo(String instanceVal) {
//visit private variable of enclosing class
System.out.println("visit the private static variable of enclosing class: ");
System.out.println(Outer.info);
System.out.println("visit the private instance variable of enclosing class: ");
System.out.println(instanceOuterInfo);
//visit private method of enclosing class
System.out.println(staticMethodOfOuter(
" Called by private instance method of instance nested class") );
System.out.println(instanceMethod(
" Called by private instance method of instance nested class") );
//命名冲突解决方案
System.out.println("Checking name conflict: ");
System.out.println("The parameter of method: " + instanceVal);
System.out.println("The instance variable of inner class: " + this.instanceVal);
System.out.println("The instance variable of enclosing class:" + Outer.this.instanceVal);
//try to modify the the value of enclosing class variable
instanceOuterInfo = "haha";
System.out.println(instanceOuterInfo);
}
}
}

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