APP
一個簡單的Java應用程序
public class Hello
{?
????public static void main (String args[ ])
????{
?????? System.out.println("這是一個簡單的應用程序");
????}
}
源程序
public class People
{
????float hight,weight;?
????String head,ear,mouth;
????void speak(String s)
????{?
?????? System.out.println(s);
????}
}
class A
{?
????public static void main(String args[])
????{
??????People zhubajie;
??????zhubajie=new People();
??????zhubajie.weight=200f;????
??????zhubajie.hight=1.70F;
??????zhubajie.head="大頭";
??????zhubajie.ear="兩只大耳朵";
??????zhubajie.mouth="一只大嘴";
??????System.out.println("重量"+zhubajie.weight+"身高" +zhubajie.hight);
??????System.out.println(zhubajie.head+zhubajie.mouth+zhubajie.ear);
??????zhubajie.speak("師傅，咱們別去西天了，改去月宮吧");
????}
}
一個簡單的Java小應用程序（Java Applet）
import java.applet.*;?
import java.awt.*;
public class boy extends Applet
{??
????public void paint(Graphics g)
????{
???? g.setColor(Color.red);???
???? g.drawString("我一邊喝著咖啡，一邊學Java呢",2,30);
???? g.setColor(Color.blue);
???? g.drawString("我學得很認真",10,50);
????}
}????
基本數據類型和數組
例子1
public class??Example2_1?
{??
????public static void main (String args[ ])
????{
???? char chinaWord='你',japanWord='ぁ';
???? int??p1=20328,p2=12358;
???? System.out.println("漢字'你'字在unicode表中的順序位置:"+(int)chinaWord);
???? System.out.println("日語'ぁ'字在unicode表中的順序位置:"+(int)japanWord);?
???? System.out.println("unicode表中第20328位置上的字符是:"+(char)p1);
???? System.out.println("unicode表中第12358位置上的字符是:"+(char)p2);?
????}
}
例子2?
public class Example2_2
{?
????public static void main (String args[ ])?
????{?
??????byte??a=120;
??????short b=255;
??????int c=2200;?
??????long d=8000;
??????float f;
??????double g=123456789.123456789;
??????b=a;
??????c=(int)d;
??????f=(float)g;?? //導致精度的損失.
??????System.out.print("a=??"+a);???
??????System.out.println(" b=??"+b);?
??????System.out.print("??c=??"+c);????
??????System.out.println("??d=??"+d);?
??????System.out.println("f=??"+f);??
??????System.out.println("g=??"+g);?
????}
}
例子3?
public class Example2_3
{?
????public static void main(String args[])
????{
???? int a[]={1,2,3,4};
???? int b[];
???? System.out.println(a[3]);
???? b=a;
???? b[3]=100;
???? System.out.println(a[3]);
???? System.out.println(b[3]);
????}
}??
運行結果：
4
100
100
運算符、表達式和語句
例子1
class Example3_1
{??
????public static void main(String args[])
????{
??????char a1='十',a2='點',a3='進',a4='攻';
??????char secret='8';
??????a1=(char)(a1^secret);???
??????a2=(char)(a2^secret);
??????a3=(char)(a3^secret);???
??????a4=(char)(a4^secret);
??????System.out.println("密文:"+a1+a2+a3+a4);
??????a1=(char)(a1^secret);???
??????a2=(char)(a2^secret);
??????a3=(char)(a3^secret);??
??????a4=(char)(a4^secret);
??????System.out.println("原文:"+a1+a2+a3+a4);
????}
}
PS:^為按位異或，按位異或兩次即變為原來。
例子2
class Example3_2
{
????public static void main(String args[])
????{
??????float x=12.56f,y;
??????if(x<=0)
??????{
????????y=x+1;
??????}
??????else if(x>0&&x<=16)
??????{
????????y=2*x+1;
??????}
??????else?
??????{
???????? y=3*x+3;
??????}
??????System.out.println(y);
????}
}
例子3
import java.applet.*;
import java.awt.*;
public class Example3_3 extends Applet
{?
????public void paint(Graphics g)
????{?
??????int x=2,y=1;
??????switch(x+y)
????????{
???????? case 1 :
???????????? g.setColor(Color.red);g.drawString("i am 1",5,10);
???????????? break;????
???????? case 2:
???????????? g.setColor(Color.blue); g.drawString("i am 2",5,10);
???????????? break;???
???????? case 3:???
????????????g.setColor(Color.green); g.drawString("i am 3",5,10);
????????????break;?????
???????? default:??g.drawString("沒有般配的",5,10);
????????}
????}
}??
例子4
import java.applet.*;
import java.awt.*;
public class Example3_4??extends Applet
{??
????public void paint(Graphics g)
????{??
??????int sum=0;?
??????for(int i=1;i<=100;i++)
????????{?
?????????? sum=sum+i;
????????}
??????g.drawString("sum= "+sum,10,20);
????}
}
例子5
class Example3_5?
{???
????public static void main(String args[])
????{ double sum=0,a=1;int i=1;
??????while(i<=20)
????????{
??????????a=a*(1.0/i);
??????????sum=sum+a;
??????????i=i+1;??????????
????????}
??????System.out.println("sum="+sum);
????}
}
例子 6
class Example3_6
{??
????public static void main(String args[])?
????{?
?????? int sum=0,i,j;
?????? for( i=1;i<=10;i++)??????????????????//計算1+3+5+7+9。
?????? {??if(i%2==0)?
??????????{
???????????? continue;??
??????????}?
??????????else
???????????? {}?
??????????sum=sum+i;
?????? }
?????? System.out.println("sum="+sum);
????}
}
例子 7
class Example3_7?
{???
????public static void main(String args[])
????{?
??????int n=23,start,end,middle;
??????int a[]={-2,1,4,5,8,12,17,23,45,56,90,100};
??????start=0;
??????end=a.length;
??????middle=(start+end)/2;
??????int count=0;
??????while(n!=a[middle])
????????{
??????????if(n>a[middle])
????????????{
??????????????start=middle;
????????????}
??????????else if(n<a[middle])
????????????{
??????????????end=middle;
????????????}
??????????middle=(start+end)/2;
??????????count++;
??????????if(count>a.length/2)
???????????? break;
???????? }
??????if(count>a.length/2)
???????? System.out.println(":"+n+"不在數組中");
??????else
???????? System.out.println(":"+n+"是數組中的第"+middle+"個元素");?
????}
}
類、對象、和接口
例子1
class XiyoujiRenwu???
{???
????float height,weight;
????String head, ear,hand,foot, mouth;
????void speak(String s)?
????{?
?????? System.out.println(s);
????}
}
class A
{??
????public static void main(String args[])
????{?
?????? XiyoujiRenwu??zhubajie;?????? //聲明對象。
?????? zhubajie=new??XiyoujiRenwu(); //為對象分配內存，使用new 運算符和默認的構造方法。
????}
}
例子2
class Point?
{?
????int x,y;
????Point(int a,int b)
????{?
?????? x=a;
?????? y=b;
????}
}
public class A?
{?
????public static void main(String args[])
????{?
??????Point p1,p2;???????????????? //聲明對象p1和p2。
??????p1=new Point(10,10);???????? //為對象分配內存，使用 new 和類中的構造方法。
??????p2=new Point(23,35);????????//為對象分配內存，使用 new 和類中的構造方法。
????}
}
例子3
class XiyoujiRenwu
{?
????float height,weight;
????String head, ear,hand,foot,mouth;
????void speak(String s)
????{?
?????? head="歪著頭";
?????? System.out.println(s);
????}
}
public class Example
{??
????public static void main(String args[])?
????{?
???????? XiyoujiRenwu??zhubajie,sunwukong;//聲明對象。
???????? zhubajie=new??XiyoujiRenwu();??//為對象分配內存,使用new 運算符和默認的構造方法。
???????? sunwukong=new??XiyoujiRenwu();
???????? zhubajie.height=1.80f;????????????????????????????????//對象給自己的變量賦值。
???????? zhubajie.weight=160f;??????
???????? zhubajie.hand="兩只黑手";
???????? zhubajie.foot="兩只大腳";?
???????? zhubajie.head="大頭";?
???????? zhubajie.ear="一雙大耳朵";?
???????? zhubajie.mouth="一只大嘴";?
???????? sunwukong.height=1.62f;????????????????????????????????//對象給自己的變量賦值。
???????? sunwukong.weight=1000f;????
???????? sunwukong.hand="白嫩小手";
???????? sunwukong.foot="兩只繡腳";?
???????? sunwukong.head="繡發飄飄";?
???????? sunwukong.ear="一對小耳";??
???????? sunwukong.mouth="櫻桃小嘴";
???????? System.out.println("zhubajie的身高："+zhubajie.height);
???????? System.out.println("zhubajie的頭："+zhubajie.head);
???????? System.out.println("sunwukong的重量："+sunwukong.weight);
???????? System.out.println("sunwukong的頭："+sunwukong.head);
???????? zhubajie.speak("俺老豬我想娶媳婦");?????????????????????? //對象調用方法。
???????? System.out.println("zhubajie現在的頭："+zhubajie.head);
???????? sunwukong.speak("老孫我重1000斤，我想騙八戒背我");???????? //對象調用方法。
???????? System.out.println("sunwukong現在的頭："+sunwukong.head);
????}
}
例子4
class 圓?
{??
????double 半徑;
????圓(double r)
????{?
?????? 半徑=r;
???? }
????double 計算面積()?
????{??
?????? return 3.14*半徑*半徑;
????}
????void 修改半徑(double 新半徑)
????{??
?????? 半徑=新半徑;
????}
????double 獲取半徑()?
????{?
????????return 半徑;
????}
}
class 圓錐?
{?
????圓 底圓;
????double 高;
????圓錐(圓 circle,double h)?
????{??
?????? this.底圓=circle;
?????? this.高=h;
????}
????double 計算體積()?
?? {???
?????? double volume;
?????? volume=底圓.計算面積()*高/3.0;
?????? return??volume;
????}
????void 修改底圓半徑(double r)?
????{??
????????底圓.修改半徑(r);
????}
????double 獲取底圓半徑()?
????{??
????????return 底圓.獲取半徑();
????}
}
class Example?
{??
????public static void main(String args[])
????{?
?????? 圓 circle=new 圓(10);
?????? 圓錐 circular=new 圓錐(circle,20);
?????? System.out.println("圓錐底圓半徑:"+circular.獲取底圓半徑());?
?????? System.out.println("圓錐的體積:"+circular.計算體積());
?????? circular.修改底圓半徑(100);
?????? System.out.println("圓錐底圓半徑:"+circular.獲取底圓半徑());
?????? System.out.println("圓錐的體積:"+circular.計算體積());??
????}
}
例子5
class 梯形?
{???
????float 上底,高;
????static float 下底;????????????????//類變量。
????梯形(float 上底,float 高)?
????{?
?????? this.上底=上底;
?????? this.高=高;
????}
????float 獲取上底()
????{??
?????? return 上底;
????}
????float 獲取下底()
????{??
?????? return 下底;
????}
}
class Example4_5?
{???
????public static void main(String args[])?
????{?
?????? 梯形 laderOne,laderTwo;????????????????????//梯形的字節碼被加載到內存。
?????? 梯形.下底=60;??????????????????????????????//通過類名操作類變量。
?????? laderOne=new 梯形(18.0f,20);
?????? laderTwo=new 梯形(9.0f,10);
?????? System.out.println("laderOne的上底:"+laderOne.獲取上底());
?????? System.out.println("laderOne的下底:"+laderOne.獲取下底());
?????? System.out.println("laderTwo的上底:"+laderTwo.獲取上底());
?????? System.out.println("laderTwo的下底:"+laderTwo.獲取下底());
????}?
}
例子6
package tom.jiafei;
public class??Example4_6?
{??
????public static void main(String args[])
????{
?????? System.out.println("我有包名");??
????}
}
例子7
import java.applet.Applet;
import java.awt.*;
public class Example extends Applet?
{??
????Button redbutton;
????public void init()
????{???
???????? redbutton=new Button("我是一個紅色的按鈕");?
???????? redbutton.setBackground(Color.red);
???????? add(redbutton);
????}
????public void??paint(Graphics g)?
????{??
???????? g.drawString("it is a button",30,50);
????}
}
例子8
import tom.jiafei.*;
class Example4_8?
{??
????public static void main(String args[])
????{??
????????Trangle trangle=new Trangle(12,3,1);
??????????????trangle.計算面積();
??????????????trangle.修改三邊(3,4,5);
??????????????trangle.計算面積();
????}
}
例子9
class Example4_9?
{???
????private int money;
????Example4_9()?
????{??
????????money=2000;
????}?
????private int getMoney()?
????{?
?????? return money;
????}
????public static void main(String args[])?
????{?
?????? Example??exa=new Example();
?????? exa.money=3000;
?????? int m=exa.getMoney();
?????? System.out.println("money="+m);
????}
}
例子10
class Father?
{??
????private int money;
????int weight=100;
????String speak(String s)?
????{?
??????return s ;
????}
}
class Son extends Father?
{???
????String hand ;
????void f()
????{
??????weight=200;
??????System.out.println(weight);
????}
}?
class Suizi extends Son
{
????String foot ;
}
public class Example4_10?
{??
????public static void main(String args[])?
????{?
?????? Son son=new Son();
?????? Suizi sunzi=new Suizi();
?????? son.hand="兩只手 ";
?????? sunzi.hand="兩小只手 ";
?????? sunzi.foot="兩只腳 ";
?????? System.out.println(son.hand);
?????? son.f();
?????? System.out.println(sunzi.weight+":"+sunzi.hand+":"+sunzi.foot);
?????? System.out.println(sunzi.speak("我是孫子"));
????}
}????
例子11
Father.java:
package tom.jiafei;
public class??Father?
{?
????int??height;
????protected int money=120;
????public?? int weight;
????protected int getMoney()?
????{??
??????return money;
????}
????void setMoney(int newMoney)?
????{??
??????money=newMoney;
????}?
}
Jerry.java:
package sun.com;
import tom.jiafei.Father;
public class Jerry extends Father??????????//Jerry和Father在不同的包中.
{??
????void f()
????{
??????money=1000;??????????????????????????//合法,
??????//height=1.89f;????????????????????????//非法，因為Jerry沒有繼承友好的height
??????System.out.println(money);??????????????//輸出結果是1000。
??????//setMoney(300);??????????????????????//非法，因為Jerry沒有繼承友好的方法setMoney。
???? int number=getMoney();????????????????//合法.
??????System.out.println(number);????????????//輸出結果是1000。
????}
????public static void main(String args[])?
????{??
?????? Jerry??jerry=new Jerry();
?????? jerry.f();
????}
}
例子
protected的進一步說明
A.java：
package tom.jiafei;
public class??A
{?
????protected int x=120;
????protected void fA()?
????{??
??????System.out.println("我是A類中的protected方法");
??????System.out.println("x="+x);
????}
}
B.java：
package sun.com;
import tom.jiafei.A;
public class B extends A
{
????protected void fB()?
????{??
??????System.out.println("我是B類中自己定義的方法");
????}
????public static void main(String args[])
????{
??????B b=new B(); //對象b在B類中.
??????b.x=1000;??//合法.?
??????b.fA();????//合法.
??????b.fB();????//合法.
????}
}
DL.java：
package sun.com;
import sun.com.B;
public class DL
{
????public static void main(String args[])
????{
?????? B b=new B(); //對象b在DL類中.
?????? b.x=1000;??//非法,因為對象b的成員變量x是從A類繼承的,但DL和A不在同一包中.?
?????? b.fA();????//非法.因為方法fA是B類從A類繼承的protected方法,但DL和A不在同一包中.
?????? b.fB();????//合法,因為方法fB是B類中自己定義的protected方法, DL類和B類在同一包中.
????}
}
Example.java
package tom.jiafei;
import sun.com.B;
public class Example
{
????public static void main(String args[])
????{
?????? B b=new B(); //對象b在Example類中.
?????? b.x=1000;??//合法,因為對象b的成員變量x是從A類繼承的,而Example和A在 同一包中.
?????? b.fA(); //合法.因為方法fA是B類從A類繼承的protected方法,而Example和A在同一包中.
?????? b.fB(); //非法,因為方法fB是B類中自己定義的protected方法,但 Example類和B類不在同一?
???????????? // 包中.
????}
}
例子12
import java.applet.*;
import java.awt.*;
class A
{??
????private int number=100;
????float f(int x,int y)?
????{??
?????? return x+y;
????}
????float g(float x,float y)?
????{?
?????? return x+y+number;
????}
}
class B extends A
{?
????float f(int x,int y)?
????{?
?????? return x*y;
????}??
}
public class Example?
{??
????public static void main(String args[])?
????{??
??????B b=new B();
??????System.out.println(b.f(2,5));?? //調用重寫的方法。
??????System.out.println(b.g(2,5));?? //b調用繼承的父類的方法。
????}?
}?
例子13
class??類人猿?
{??
????private int n=100;
????void crySpeak(String s)?
????{??
??????System.out.println(s);?
????}??
}
class People extends 類人猿?
{?
????void computer(int a,int b)
????{??
?????? int c=a*b;
?????? System.out.println(c);?
????}
void crySpeak(String s)?
????{?
?????? System.out.println("**"+s+"**");?
????}??
}
class Example
{??public static void main(String args[])?
????{??
?????? 類人猿 monkey=new People();?? //monkey是People對象的上轉型對象。
?????? monkey.crySpeak("I love this game");
?????? //monkey.n=23;????????????????//非法,因為子類未繼承n.
?????? //monkey.computer(12,19);???? //非法,computer是子類新增的功能.
?????? People people=(People)monkey; //把上轉型對象強制轉化為子類的對象。
?????? people.computer(10,10);
????}
}
例子14
class??動物?
{??void cry()?
????{
????}
}
class 狗 extends 動物 {?
{??void cry()?
????{??System.out.println("汪汪.....");?
????}??
}
class 貓 extends 動物?
{??void cry()?
????{??System.out.println("喵喵.....");?
????}??
}
class Example4_14?
{??public static void main(String args[])?
????{??動物 dongwu;
?????? if(Math.random()>=0.5)?????
??????????{
????????????dongwu=new 狗();
????????????dongwu.cry();?
??????????}
?????? else
???????? {
?????????? dongwu=new 貓();
????????????ongwu.cry();
??????????}
????}
}
例子15
abstract class 圖形?
{??
????public abstract double 求面積();
}
class 梯形 extends 圖形?
{?
????double a,b,h;
????梯形(double a,double b,double h)
????{??
?????? this.a=a;this.b=b;this.h=h;
????}
????public double 求面積()?
????{??
???????? return((1/2.0)*(a+b)*h);
????}
}
class 圓形 extends 圖形?
{??
????double r;
????圓形(double r)
????{??
?????? this.r=r;
????}
????public double 求面積()
????{??
?????? return(3.14*r*r);
????}
}
class 堆?
{??
????圖形 底;
????double 高;
????堆(圖形 底,double 高)?
????{?
????????this.底=底;
????????this.高=高;
????}
????void 換底(圖形 底)?
????{
????????this.底=底;
????}
????public double 求體積()?
????{??
?????? return (底.求面積()*高)/3.0;
????}
}
public class Example4_15
{?
????public static void main(String args[])?
????{?
?????? 堆 zui;
?????? 圖形 tuxing;
?????? tuxing=new 梯形(2.0,7.0,10.7);
?????? System.out.println("梯形的面積"+tuxing.求面積());
?????? zui=new??堆(tuxing,30);
?????? System.out.println("梯形底的堆的體積"+zui.求體積());
?????? tuxing=new 圓形(10);
?????? System.out.println("半徑是10的圓的面積"+tuxing.求面積());
?????? zui.換底(tuxing);
?????? System.out.println("圓形底的堆的體積"+zui.求體積());
????}
}
例子16
class Student?
{??
????int number;String name;
????Student(int number,String name)?
????{??
????????this.number=number;
????????this.name=name;
????????System.out.println("I am "+name+ "my number is "+number);
????}
}
class Univer_Student extends Student?
{??
????boolean 婚否;
????Univer_Student(int number,String name,boolean b)?
????{
?????? super(number,name);
?????? 婚否=b;
?????? System.out.println("婚否="+婚否);
????}
}
public class Example4_16?
{?
????public static void main(String args[])?
????{??
??????Univer_Student zhang=new Univer_Student(9901,"和曉林",false);
????}
}
例子17
class Sum?
{??
????int n;
????float f()?
????{??
?????? float sum=0;
?????? for(int i=1;i<=n;i++)
?????????? sum=sum+i;
?????????? return sum;??
????}
}
class Average extends Sum?
{??
????int n;??
????float f()?
????{??
?????? float c;
?????? super.n=n;
?????? c=super.f();
?????? return c/n;?
????}
????float g()?
????{?
?????? float c;
?????? c=super.f();
?????? return c/2;?
????}
}
public class Example4_17
{??
????public static void main(String args[])?
????{??
?????? Average aver=new Average();
?????? aver.n=100;
?????? float result_1=aver.f();
?????? float result_2=aver.g();
?????? System.out.println("result_1="+result_1);
?????? System.out.println("result_2="+result_2);
????}
}
例子18
import java.applet.*;
import java.awt.*;
interface Computable?
{??
????final int MAX=100;
????void speak(String s);
????int f(int x);
????float g(float x,float y);
}
class China implements Computable?
{?
????int xuehao;
????public??int f(int x)?? //不要忘記public關鍵字。
????{?
?????? int sum=0;
?????? for(int i=1;i<=x;i++)
??????????{?
????????????sum=sum+i;
??????????}
?????? return sum;
????}
????public float g(float x,float y)
????{??
???????? return 6;?????????????????? //至少有return語句。??
????}
????public void speak(String s)?
????{?
????}
}
class Japan implements Computable?
{?
????int xuehao;
????public int f(int x)?
????{??
????????return 68;?
????}
????public??float g(float x,float y)?
????{?
????????return x+y;
????}
public void speak(String s)?
????{????????????????????????????//必須有方法體，但體內可以沒有任何語句。
????}
}
public class Example4_18??extends Applet?
{?
????China Li;
????Japan Henlu;
????public void init()?
????{??
?????? Li=new China();???
?????? Henlu=new Japan();??
?????? Li.xuehao=991898;
?????? Henlu.xuehao=941448;
????}
????public void paint(Graphics g)?
????{?
?????? g.drawString("xuehao:"+Li.MAX+Li.xuehao+"從1到100求和"+Li.f(100),10,20);
?????? g.drawString("xuehao:"+Henlu.MAX+Henlu.xuehao+"加法"+Henlu.g(2.0f,3.0f),10,40);
????}
}???
例子19
interface??收費?
{?
????public void??收取費用();
}
interface??調節溫度?
{?
????public void??controlTemperature();
}
class 公共汽車 implements 收費?
{??
????public??void 收取費用()?
????{??
?????? System.out.println("公共汽車:一元/張,不計算公里數");
????}
}?
class 出租車 implements 收費, 調節溫度
{??
????public void 收取費用()?
????{??
?????? System.out.println("出租車:1.60元/公里,起價3公里");
????}
????public void??controlTemperature()
????{??
?????? System.out.println("安裝了Hair空調");
????}
}
class 電影院 implements 收費,調節溫度
{??
????public void 收取費用()
????{?
????????System.out.println("電影院:門票,十元/張");
????}
????public void??controlTemperature()
????{??
????????System.out.println("安裝了中央空調");
????}
}
class Example4_19
{?
????public static void main(String args[])
????{??
?????? 公共汽車 七路=new 公共汽車();
?????? 出租車?? 天宇=new 出租車();
?????? 電影院?? 紅星=new 電影院();
?????? 七路.收取費用();
?????? 天宇.收取費用();
?????? 紅星.收取費用();
?????? 天宇.controlTemperature();
?????? 紅星.controlTemperature();
????}
}
例子20
interface??ShowMessage?
{??
????void 顯示商標(String s);
}
class TV implements ShowMessage?
{??
????public void 顯示商標(String s)?
????{?
?????? System.out.println(s);
????}
}
class PC implements ShowMessage?
{?
????public void 顯示商標(String s)?
????{??
????????System.out.println(s);
????}
}
public class Example4_20?
{??
????public static void main(String args[])
????{?
?????? ShowMessage sm;??????????????????//聲明接口變量。
?????? sm=new TV();???????????????????? //接口變量中存放對象的引用。
?????? sm.顯示商標("長城牌電視機");??????//接口回調。
?????? sm=new PC();???????????????????? //接口變量中存放對象的引用。
?????? sm.顯示商標("聯想奔月5008PC機"); //接口回調。
????}?
}
例子21
interface??Computerable
{?
????public??double 求面積();
}
class 梯形 implements Computerable?
{?
????double a,b,h;
????梯形(double a,double b,double h)?
????{??
????????this.a=a;this.b=b;this.h=h;
????}
????public double 求面積()?
????{??
????????return((1/2.0)*(a+b)*h);
????}
}
class 圓形 implements Computerable?
{??
????double r;
????圓形(double r)?
????{??
?????? this.r=r;
????}
????public double 求面積()?
????{
?????? return(3.14*r*r);
????}
}
class 堆?
{?
????Computerable 底;?????????? //聲明一個接口變量,可以回調"求面積"方法。
????double 高;
????堆(Computerable 底,double 高)?
????{??
?????? this.底=底;
?????? this.高=高;
????}
????void 換底(Computerable 底)?
????{??
????????this.底=底;
????}
???? public double 求體積()
????{??
??????return (底.求面積()*高)/3.0;
????}
}
public class Example4_21
{??
????public static void main(String args[])
????{??
?????? 堆 zui;
?????? Computerable bottom;
?????? bottom=new 梯形(2.0,7.0,10.7); //接口變量中存放對象的引用。
?????? System.out.println("梯形的面積"+bottom.求面積()); //bottom接口回調，求面積。
?????? zui=new??堆(bottom,30);
?????? System.out.println("梯形底的堆的體積"+zui.求體積());
?????? bottom=new 圓形(10);??//接口變量中存放對象的引用。
?????? System.out.println("半徑是10的圓的面積"+bottom.求面積());
?????? zui.換底(bottom);
?????? System.out.println("圓形底的堆的體積"+zui.求體積());
????}
}
例子22
public class Example4_22
{??
????public static void main(String args[])?
????{??
??????int n=0,m=0,t=0;
??????try
???????? {??
????????????t=9999;
????????????m=Integer.parseInt("8888");
????????????n=Integer.parseInt("12s3a");????//發生異常,轉向catch。
????????????System.out.println("我沒有機會輸出");
???????? }
??????catch(Exception e)
???????? {
?????????? System.out.println("發生異常");
?????????? n=123;
???????? }
??????System.out.println("n="+n+",m="+m+",t="+t);
????}
}
例子23
class MyException extends Exception
{
????String message;
????MyException()
????{
????message="數字不是正數";
????}
???? public String toString()
????{
??????return message;
????}
}
class YourException extends Exception
{
????String message;
????YourException()
????{
????message="數字不是偶數";
????}
public String toString()
????{
??????return message;
????}
}
class A
{
????public void f(int n) throws MyException,YourException
????{
??????if(n<0)
????????{
??????????throw(new??MyException());???????????? //拋出異常，結束方法的執行。
????????}
??????if(n%2!=0)
????????{
??????????throw(new??YourException());?????????? //拋出異常，,結束方法的執行。
????????}
??????double number=Math.sqrt(n);
??????System.out.println(number);
????}
public static void main(String args[])
????{
??????A a=new A();
???? try?
???????? {
?????????? a.f(9);
???????? }
??????catch(MyException e)
???????? {
????????????System.out.println(e.toString());
???????? }
??????catch(YourException e)
???????? {
????????????System.out.println(e.toString());
???????? }
?????? try?
???????? {
?????????? a.f(-8);
???????? }
??????catch(MyException e)
???????? {
????????????System.out.println(e.toString());
???????? }
??????catch(YourException e)
???????? {
????????????System.out.println(e.toString());
???????? }
?????? try?
???????? {
?????????? a.f(16);
???????? }
??????catch(MyException e)
???????? {
????????????System.out.println(e.toString());
???????? }
?????? catch(YourException e)
???????? {
????????????System.out.println(e.toString());
???????? }
????}
}
常用實用類
例子1
class Example5_1
{
????public static void main(String args[])
????{
?????? String s1,s2;
?????? s1=new String("we are students");
?????? s2=new String("we are students");
?????? System.out.println(s1.equals(s2));????//輸出結果是：true。
?????? System.out.println(s1==s2);???????? //輸出結果是：false
?????? String s3,s4;?
?????? s3="how are you";
?????? s4="how are you";?
?????? System.out.println(s3.equals(s4));????//輸出結果是：true。
?????? System.out.println(s3==s4);???????? //輸出結果是：true。?????
????}
}
例子2
class Example5_2?
{?? public static void main(String args[])
????{??int number=0;?
?????? String s="student;entropy;engage,english,client";
?????? for(int k=0;k<s.length();k++)
????????{??if(s.regionMatches(k,"en",0,2))
???????????? {??number++;
???????????? }
???????? }?
?????? System.out.println("number="+number);
????}
}
例子3
class Example5_3?
{??public static void main(String args[])?
????{??String a[]={"boy","apple","Applet","girl","Hat"};
?????? for(int i=0;i<a.length-1;i++)?
??????????{for(int j=i+1;j<a.length;j++)?
????????????{??if(a[j].compareTo(a[i])<0)?
?????????????? {??String temp=a[i];
?????????????????? a[i]=a[j];
?????????????????? a[j]=temp;
????????????????}
????????????}?
???????? }
??????for(int i=0;i<a.length;i++)?
???????? {??System.out.print("??"+a[i]);
???????? }
????}
}
例子4
public class Example5_4
{??public static void main(String args[])?
????{??double n,sum=0.0 ;
?????? for(int i=0;i<args.length;i++)?
????????{??sum=sum+Double.parseDouble(args[i]);
????????}
??????n=sum/args.length;
??????System.out.println("平均數:"+n);
????}
}
例子5
import java.util.Date;?
import java.awt.*;
public class Example5_5
{??
????public static void main(String args[])
????{?
??????Date date=new Date();
??????Button button=new Button("確定");
??????System.out.println(date.toString());
??????System.out.println(button.toString());??
????}
}
例子6
class Example5_6
{???
????public static void main(String args[])
????{??
?????? char c[],d[];
?????? String s=”巴西足球隊擊敗德國足球隊”;
?????? c=new char[2];
?????? s.getChars(5,7,c,0);
?????? System.out.println©;
?????? d=new char[s.length()];
?????? s.getChars(7,12,d,0);
?????? s.getChars(5,7,d,5);
?????? s.getChars(0,5,d,7);
?????? System.out.println(d);
????}
}
例子7
class Example5_7
{??
????public static void main(String args[])?
????{?
?????? String s="列車時刻表";
?????? char a[]=s.toCharArray();
?????? for(int i=0;i<a.length;i++)
???????? {??a[i]=(char)(a[i]^'t');
???????? }
?????? String secret=new String(a);?
??????System.out.println("密文:"+secret);
??????for(int i=0;i<a.length;i++)
????????{??
????????????a[i]=(char)(a[i]^'t');
????????}
????String code=new String(a);??
????System.out.println("原文:"+code);
????}
}
例子8
public class Example5_8
{?
????public static void main(String args[])
????{??
?????? byte d[]="你我他".getBytes();???????????
?????? System.out.println("數組d的長度是(一個漢字占兩個字節):"+d.length);
?????? String s=new String(d,0,2);
?????? System.out.println(s);
????}
}
例子9
class Example5_9
{
????public static void main(String args[])
????{
??????StringBuffer str=new StringBuffer();
?????? str.append("大家好");
?????? System.out.println("str:"+str);
??????System.out.println("length:"+str.length());
?????? System.out.println("capacity:"+str.capacity());?
?????? str.append("我們大家都很愿意學習Java語言");
?????? System.out.println("str:"+str);
?????? System.out.println("length:"+str.length());
??????System.out.println("capacity:"+str.capacity());?
?????? StringBuffer sb=new StringBuffer("Hello");
?????? System.out.println("length:"+sb.length());
?????? System.out.println("capacity:"+sb.capacity());?
????}
}
例子10
class Example5_10
{
????public static void main(String args[])
????{
?????? StringBuffer str=new StringBuffer("我們大家都很愿意學習Java語言");
?????? str.setCharAt(0 ,'w');?
?????? str.setCharAt(1 ,'e');
?????? System.out.println(str);?
?????? str.insert(2, " all");
?????? System.out.println(str);
?????? str.delete(6,8);
?????? System.out.println(str);
?????? int index=str.indexOf("都");
?????? str.replace(index,str.length()," love java");
?????? System.out.println(str);
????}
}
例子11
import java.util.*;
public class Example5_11?
{??
????public static void main(String args[])
????{??
?????? String s="we are stud,ents";
?????? StringTokenizer fenxi=new StringTokenizer(s," ,"); //空格和逗號做分
?????? int number=fenxi.countTokens();
?????? while(fenxi.hasMoreTokens())?
????????{?
?????????? String str=fenxi.nextToken();
?????????? System.out.println(str);
?????????? System.out.println("還剩"+fenxi.countTokens()+"個單詞");
????????}
??????System.out.println("s共有單詞："+number+"個");
????}?
}
例子12
import java.util.*;
public class Example5_12
{??public static void main(String args[])?
?? {??String s=new String("abcABC123");
??????System.out.println(s);????
??????char a[]=s.toCharArray();
??????for(int i=0;i<a.length;i++)
?????? { if(Character.isLowerCase(a[i]))?
??????????{ a[i]=Character.toUpperCase(a[i]);
??????????}
?????? else if(Character.isUpperCase(a[i]))?
??????????{ a[i]=Character.toLowerCase(a[i]);
??????????}
?????? }
???? s=new String(a);
???? System.out.println(s);??????
?? }?
}
例子13
import java.util.Date;
import java.text.SimpleDateFormat;
class Example5_13
{??
????public static void main(String args[])
????{?
??????Date nowTime=new Date();
??????System.out.println("現在的時間:"+nowTime);
??????SimpleDateFormat matter1=new SimpleDateFormat("yyyy年MM月dd日 北京時間");
??????System.out.println("現在的時間:"+matter1.format(nowTime));
??????SimpleDateFormat matter2=
??????new SimpleDateFormat("yyyy年MM月Edd日HH時mm分ss秒 北京時間");
??????System.out.println("現在的時間:"+matter2.format(nowTime));
??????SimpleDateFormat matter3=
??????new SimpleDateFormat("北京時間dd日HH時MMM ss秒mm分EE");
??????System.out.println("現在的時間:"+matter3.format(nowTime));
??????long time=-1800;
??????Date date=new Date(time);
??????System.out.println("-1800秒表示的日期時間是："+date);
????}
}
例子14
import java.util.*;
class Example5_14
{?
????public static void main(String args[])?
?? {??
??????Calendar calendar=Calendar.getInstance(); //創建一個日歷對象。
??????calendar.setTime(new Date());??????????//用當前時間初始化日歷時間。
??????String 年=String.valueOf(calendar.get(Calendar.YEAR)),
???????????? 月=String.valueOf(calendar.get(Calendar.MONTH)+1),
???????????? 日=String.valueOf(calendar.get(Calendar.DAY_OF_MONTH)),
???????????? 星期=String.valueOf(calendar.get(Calendar.DAY_OF_WEEK)-1);
??????int hour=calendar.get(Calendar.HOUR_OF_DAY),
??????????minute=calendar.get(Calendar.MINUTE),
??????????second=calendar.get(Calendar.SECOND);
??????System.out.println("現在的時間是：");
??????System.out.println(""+年+"年"+月+"月"+日+"日 "+ "星期"+星期);
??????System.out.println(""+hour+"時"+minute+"分"+second+"秒");
??????calendar.set(1962,5,29);??//將日歷翻到1962年6月29日,注意5表示六月。
??????long time1962=calendar.getTimeInMillis();
??????calendar.set(2003,9,5);??//將日歷翻到2003年10月5日。9表示十月。
??????long time2003=calendar.getTimeInMillis();
??????long 相隔天數=(time2003-time1962)/(1000*60*60*24);
??????System.out.println("2003年10月5日和1962年6月29日相隔"+相隔天數+"天");
?? }??
}
例子 15
import java.util.*;?
class Example5_15?
{?
????public static void main(String args[])
{?
?? System.out.println(" 日 一 二 三 四 五 六");
?????? Calendar 日歷=Calendar.getInstance();????????
?????? 日歷.set(2004,9,1);??//將日歷翻到2004年10月1日,注意0表示一月。
?????? //獲取1日是星期幾(get方法返回的值是1表示星期日,星期六返回的值是7):
?????? int 星期幾=日歷.get(Calendar.DAY_OF_WEEK)-1;
?????? String a[]=new String[星期幾+31];???????????? //存放號碼的一維數組
?????? for(int i=0;i<星期幾;i++)
???????????? {
????????????????a[i]="**";
???????????? }
?????? for(int i=星期幾,n=1;i<星期幾+31;i++)
???????????? {?
?????????????? if(n<=9)
??????????????????a[i]=String.valueOf(n)+" ";
?????????????? else
??????????????????a[i]=String.valueOf(n) ;
?????????????? n++;
???????????? }??
??????//打印數組：
??????for(int i=0;i<a.length;i++)
?????? {?
??????????if(i%7==0)
??????????{?
???????????? System.out.println("");??????//換行。
??????????}
???????? System.out.print(" "+a[i]);
??????}?
?? }?
}
例子 16
import java.text.NumberFormat;
class Example5_16
{?
????public static void main(String args[])
????{??
??????double a=Math.sqrt(5);
??????System.out.println("格式化前："+a);
??????NumberFormat f=NumberFormat.getInstance();
??????f.setMaximumFractionDigits(5);
??????f.setMinimumIntegerDigits(3);
??????String s=f.format(a);
??????System.out.println("格式化后："+s);
??????System.out.println("得到的隨機數：");
??????int number=8;
??????for(int i=1;i<=20;i++)
?????? {?
???????? int randomNumber=(int)(Math.random()*number)+1;//產生1到8之間的隨機數。
???????? System.out.print(" "+randomNumber);
???????? if(i%10==0)
???????????? System.out.println("");
?????? }
????}?
}
例子17
import java.util.*;
class Example5_17
{
????public static void main(String args[])
????{?
??????Vector vector=new Vector();?
??????for(int i=1;i<=18;i++)
??????{
????????vector.add(new Integer(i));?????? //向量填加18個整數對象.
??????}
??????int a[]=new int[vector.size()];
??????int i=0;
??????while(vector.size()>0)??????????????
??????{??
????????int number=(int)(Math.random()*vector.size());???
????????Integer integer=(Integer)vector.elementAt(number);
????????a[i]=integer.intValue();????????????????????//得到整數對象中的int數.
????????vector.removeElementAt(number);????????????//向量移掉number處的整數對象.
????????i++;
?????? }
??????for(i=0;i<18;i++)
??????{
???????? System.out.print(" "+a[i]);
?????? }
????}
}
例子18
import java.util.*;
public class Example5_18
{
????public??static void main(String args[])
????{?
??????LinkedList mylist=new LinkedList();
??????mylist.add("is");?
??????mylist.add("a");
??????int number=mylist.size();
??????System.out.println("現在鏈表中有"+number+"個節點:");
??????for(int i=0;i<number;i++)
????????{
?????????? String temp=(String)mylist.get(i);
?????????? System.out.println("第"+i+"節點中的數據:"+temp);
????????}
???? mylist.addFirst("It");
???? mylist.addLast("door");
資源：
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