java类，对象

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定义一个类

package array;

public class Cricle {

double radius;

public Cricle() {
  this.radius = 1.0;
}

public Cricle(double r) {
  this.radius = r;
}

public double getRadius() {
  return radius;
}

public void setRadius(double radius) {
this.radius = radius;
}

public double getArea() {

  return Math.PI*radius*radius;

}

}

对类进行使用

package array;
/*类和对象的使用
*定义好的类，可以在创建对象以后，用"对象名.方法名"来调用类中的方法，用"对象名.属性"来调用类中的属性值，
*static定义的变量，每次改变后的值会覆盖住先前的值，
*/
public class TestCricle {

public static void main(String[] args) {
  //改变圆的半径，获取圆的面积


  Cricle cricle1 = new Cricle();//创建对象，调用的是public Cricle()中的值
  System.out.println("the radius is "+cricle1.radius);
  System.out.println("the areas is "+cricle1.getArea());

  Cricle cricle2 = new Cricle(12.0);//调用了public Cricle(double r)进行传入半径为12
  System.out.println("the radius2 is "+cricle2.radius);
  System.out.println("the areas2 is "+cricle2.getArea());

  Cricle cricle3 = new Cricle();//创建对象，调用的是public Cricle()中的值
  cricle3.radius = 100;
  System.out.println("the radius2 is "+cricle3.radius);
  System.out.println("the areas2 is "+cricle3.getArea());

  System.out.println("the radius2 is "+cricle1.radius);
  System.out.println("the areas2 is "+cricle1.getArea());
}

}

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