介绍嵌套类和内部类

// Demonstrate an inner class.
class Outer {
int outer_x = 100; 
void test() { 
Inner inner = new Inner();
inner.display();
} 
// this is an inner class class Inner { void display() 
{System.out.println("display: outer_x = " + outer_x); }}} 
class InnerClassDemo {
public static void main(String args[]) { 
Outer outer = new Outer();
outer.test();
}
} 

display: outer_x = 100 

// This program will not compile.
class Outer {
int outer_x = 100; 
void test() { 
Inner inner = new Inner();
inner.display();
} 
// this is an inner class
class Inner { 
int y = 10; // y is local to Inner
void display() {
System.out.println("display: outer_x = " + outer_x); 
}
}
void showy() { System.out.println(y); // error，y not known here!}} 
class InnerClassDemo {
public static void main(String args[]) { 
Outer outer = new Outer();
outer.test();
}
} 

// Define an inner class within a for loop.
class Outer {
int outer_x = 100; 
void test() { for(int i=0; i<10; i++) { class Inner { void display() 
{System.out.println("display: outer_x = " + outer_x); 
}
}
Inner inner = new Inner(); 
inner.display();
}
}
} 
class InnerClassDemo {
public static void main(String args[]) { 
Outer outer = new Outer();
outer.test();
}
} 

display: outer_x = 100
display: outer_x = 100
display: outer_x = 100 
display: outer_x = 100
display: outer_x = 100
display: outer_x = 100
display: outer_x = 100
display: outer_x = 100
display: outer_x = 100
display: outer_x = 100