java之数据域封装set、get方法

复习package

javac Jpro\Circles3.java

javac Jpro\Demo032901.java

java Jpro.Demo032901

Cirlces3类的代码如下：

package Jpro;
public class Circles3{
private double radius = 1;
private static int numberOfObjects = 0;
public Circles3(){
numberOfObjects++;
}
public Circles3( double newRadius ){
radius = newRadius;
numberOfObjects++;
}
public double getRadius(){
return radius;
}
public void setRadius( double newRadius ){
radius = ( newRadius >= 0 )?newRadius:0;
}
public static int getNumberOfObject(){
return numberOfObjects;
}
public double getArea(){
return radius * radius * Math.PI;
}
}

Demo032901.java主调函数类

package Jpro;
public class Demo032901{
public static void main( String [] args ){
Circles3 myCircle = new Circles3( 5.0 );
System.out.println( " radius = " + myCircle.getRadius() );
System.out.println( "area = " + myCircle.getArea() );

myCircle.setRadius( ( myCircle.getRadius() +10)  );
System.out.println( " radius = " + myCircle.getRadius() );
System.out.println( "area = " + myCircle.getArea() );
System.out.println( "the number of objects is " + Circles3.getNumberOfObject() );
}
}