java入门小程序

一个简单的Java应用程序public class Hello{public static void main (String args[ ]){System.out.println("这是一个简单的应用程序");}}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="大头";zhubajie.ear="两只大耳朵";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("师傅，咱们别去西天了，改去月宫吧");}}一个简单的Java小应用程序（Java Applet）import java.applet.*;import java.awt.*;public class boy extends Applet{public void paint(Graphics g)g.setColor(Color.red);g.drawString("我一边喝着咖啡，一边学Java呢",2,30);g.setColor(Color.blue);g.drawString("我学得很认真",10,50);}}基本数据类型和数组例子1public class Example2_1{public static void main (String args[ ]){char chinaWord='你',japanWord='ぁ';int p1=20328,p2=12358;System.out.println("汉字\'你\'字在unicode表中的顺序位置:"+(int)chinaWord);System.out.println("日语\'ぁ\'字在unicode表中的顺序位置:"+(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2public 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; //导致精度的损失.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3public 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]);}}运行结果：4100100运算符、表达式和语句例子1class Example3_1{public static void main(String args[]){char a1='十',a2='点',a3='进',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);}}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3import 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("没有般配的",5,10);}}例子4import 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5class 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6class Example3_6{public static void main(String args[]){int sum=0,i,j;for( i=1;i<=10;i++) //计算1+3+5+7+9。

{ if(i%2==0){continue;}else{}sum=sum+i;}System.out.println("sum="+sum);}}例子7class 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+"不在数组中");elseSystem.out.println(":"+n+"是数组中的第"+middle+"个元素");}}类、对象、和接口例子1class 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; //声明对象。

zhubajie=new XiyoujiRenwu(); //为对象分配内存，使用new 运算符和默认的构造方法。

}}例子2class 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; //声明对象p1和p2。