package封裝實例

建立Circle.java和Square.java以及同目錄的Test資料夾
Circle.java

package Test;
public class Circle {
        double radius;

        public Circle(double r){
       radius=r;
 }

 public double area(){
                      return radius*radius*Math.PI;
 }

 public double perimeter(){
                      return radius*2*Math.PI;
 }
}

Square.java

package Test;
public class Square {
        double size;

        public Square(double s){
       size=s;
 }

 public double area(){
                      return size*size;
 }

 public double perimeter(){
                      return size*4;
 }
}

輸入指令 javac -d /Test Circle.java
輸入指令 javac -d /Test Square.java
將資料封裝在/Test/Test裡面並建立main.java在/Test裡(封裝資料夾外) 即可讀取

class main{
 static public void main(String argv[]){
  Test.Circle c = new Test.Circle(5.6);    // generate a Circle object
                Test.Square s = new Test.Square(7.3);    // generate a Square object

                                // Output Circle's  area & perimeter (raduis is 5.6)
  System.out.println("Circle's area: "+c.area());
  System.out.println("Circle's perimeter: "+c.perimeter());
                                // Output Square's  area & perimeter (size is 7.3)
  System.out.println("Square's area: "+s.area());
  System.out.println("Square's perimeter: "+s.perimeter());
                }
}