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1、1例子例子 9class Fibi public long fibinacii(int n) long c=0;if(n=1|n=2)c=1;elsec=fibinacii(n-1)+fibinacii(n-2); return c; public class Example4_9 public static void main(String args) Fibi a=new Fibi(); for(int i=1;ii/2) System.out.print(“ 素数：“+i); 例子例子 12import java.applet.Applet;import java.awt.*;publi
2、c class Example4_12 extends Applet Button redbutton;public void init() redbutton=new Button(“我是一个红色的按钮“); redbutton.setBackground(Color.red);add(redbutton);public void paint(Graphics g) g.drawString(“it is a button“,30,50);3例子例子 13import tom.jiafei.*; /引入包 tom.jiafei 中的类。 public class Example4_13 pu
3、blic static void main(String args) PrimNumber num=new PrimNumber();/用包 tom.jiafei 中的类创建对象。String a=“ok“;System.out.println(a0);num.main(a); 例子例子 14public class Example4_14 public static void main(String args) PrimNumber num=new PrimNumber();/要保证 PrimNuber 类和 Example4_14 类在同一 目录中String a=“ok“;System.
4、out.println(a0);num.main(a);例子例子 15Trangel.java：package tom.jiafei; public class Trangle double sideA,sideB,sideC;boolean boo;public Trangle(double a,double b,double c) sideA=a;sideB=b;sideC=c;if(a+bcboo=true; else System.out.println(“我不是一个三角形“);boo=false;public void 计算面积() if(boo) double p=(sideA+s
5、ideB+sideC)/2.0;double area=Math.sqrt(p*(p-sideA)*(p-sideB)*(p-sideC) ;System.out.println(“面积是:“+area);else System.out.println(“不是一个三角形,不能计算面积“); public void 修改三边(double a,double b,double c) sideA=a;sideB=b;sideC=c;if(a+bc else boo=false; Example4_15.java:import tom.jiafei.*; class Example4_15 publi
6、c static void main(String args) Trangle trangle=new Trangle(12,3,1);trangle.计算面积();trangle.修改三边(3,4,5);5trangle.计算面积(); 例子例子 16class Example4_16 private int money;Example4_16() money=2000; private int getMoney() return money; public static void main(String args) Example4_16 exa=new Example4_16();exa
7、.money=3000;int m=exa.getMoney();System.out.println(“money=“+m);例子例子 17import java.applet.*; import java.awt.*; class Father private int money;float weight,height;String head;String speak(String s) return s ; class Son extends Father String hand ,foot; public class Example4_17 extends Applet Son boy
8、;6public void init() boy=new Son();boy.weight=1.80f; boy.height=120f;boy.head=“一个头“; boy.hand=“两只手 “;boy.foot=“两只脚“;public void paint(Graphics g) g.drawString(boy.speak(“我是儿子“),5,20);g.drawString(boy.hand+boy.foot+boy.head+boy.weight+boy.height,5,40); 例子例子 18Father.java:package tom.jiafei; public cl
9、ass Father int height;protected int money;public int weight;public Father(int m) money=m;protected int getMoney() return money;void setMoney(int newMoney) money=newMoney; Jerry.java:package ; import tom.jiafei.Father;7public class Jerry extends Father /Jerry 和 Father 在不同的包中. public Jerry() super(20)
10、;public static void main(String args) Jerry jerry=new Jerry();jerry.height=12; /非法，因为 Jerry 没有继承友好的 height。jerry.weight=200; /合法。jerry.money=800; /合法。int m=jerry.getMoney(); /合法。.jerry.setMoney(300); /非法，因为 Jerry 没有继承友好的方法 setMoney。System.out.println(“m=“+m); 例子例子 19import java.applet.*; import java
11、.awt.*; class Chengji float f(float x,float y) return x*y; class Xiangjia extends Chengji float f(float x,float y) return x+y ; public class Example4_19 extends Applet Xiangjia sum;public void init() sum=new Xiangjia();public void paint(Graphics g) g.drawString(“sum=“+sum.f(4,6),100,40); 8例子例子 20imp
12、ort java.applet.*; import java.awt.*; class Area float f(float r ) return 3.14159f*r*r;float g(float x,float y) return x+y; class Circle extends Area float f(float r) return 3.14159f*2.0f*r; public class Example4_20 extends Applet Circle yuan;public void init() yuan=new Circle(); public void paint(G
13、raphics g) g.drawString(“yuan= “+yuan.f(5.0f),5,20); /调用子类重写的方法 f。g.drawString(“ “+yuan.g(2.0f,8.0f),5,40); /调用继承父类的方法 g。 例子例子 21class 类人猿 private int n=100;void crySpeak(String s) System.out.println(s); class People extends 类人猿 9 void computer(int a,int b) int c=a*b;System.out.println(c); void cryS
14、peak(String s) System.out.println(“*“+s+“*“); class Example4_21 public static void main(String args) 类人猿 monkey=new People(); /monkey 是 People 对象的上转型对象。monkey.crySpeak(“I love this game“);People people=(People)monkey; /把上转型对象强制转化为子类的对象。puter(10,10); 例子例子 22class 动物 void cry() class 狗 extends 动物 void
15、 cry() System.out.println(“汪汪.“); class 猫 extends 动物 void cry() System.out.println(“喵喵.“); class Example4_22 public static void main(String args) 动物 dongwu;if(Math.random()=0.5) 10dongwu=new 狗();dongwu.cry(); elsedongwu=new 猫();ongwu.cry(); 例子例子 23abstract class 图形 public abstract double 求面积(); class 梯形 extends 图形 double a,b,h;梯形(d
