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如何例項化 java 內部類

package practive_java;

class cow {
  private double weight;
  public cow() {
   weight=0;
  }
  public cow(double data) {
   weight=data;
 }
 
 protected class cowleg {
    private String color;
    private double length;
    public cowleg(double length, String color) {
     this.length=length;
     this.color=color;
    }
    public void info() {
     System.out.println("current cow color " + color);
     System.out.println("current cow leg length " + length);
     System.out.println("current cow weight " + weight);
     } 
   }
 
  public void display(){
   cowleg cl=new cowleg(1.12,"black");
   cl.info();
  }
 }

public class practice {
 //初始化快
 {
   a=6;   
  }
 
  int a=9;

 public static void main(String[] args) {
  // TODO Auto-generated method stub
  System.out.println("practice.a=" + (new practice()).a); //OUTPUT 9
  

 cow mycow = new cow(23.5);
  mycow.display();
 

 //例項化內部類cowleg , this inner class must be declared as protected or public 
  cow mycow2 = new cow(23.4);
  cow.cowleg myleg= mycow2.new cowleg(12.4,"red");
  myleg.info();
 }
}