java(基础知识练习)

第二章标识符、关键字和数据类型例子1public class Example2_1{ public static void main (String args[ ]){ char chinaWord='你',japanWord='ぁ';int p1=36328,p2=38358;System.out.println("汉字\'你\'在unicode表中的顺序位置:"+(int)chinaWord);System.out.println("日语\'ぁ\'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 Array { public static void main (String args[ ]){ int c=2200;long d=8000;float f;double g=123456789.123456789;c=(int)d;f=(float)g; //导致精度的损失.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[]={100,200,300};int b[]={10,11,12,13,14,15,16};b=a;b[0]=123456;System.out.println("数组a:"+a[0]+","+a[1]+","+a[2]);System.out.println("数组b:"+b[0]+","+b[1]+","+b[2]);System.out.println("数组b的长度:"+b.length);}}第三章运算符、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);}}密文:卹炁迣攃原文:十点进攻例子2class Example3_2{ public static void main(String args[]){ int x,y=10;if(((x=0)==0)||((y=20)==20)){ System.out.println("现在y的值是:"+y);}int a,b=10;if(((a=0)==0)|((b=20)==20)){ System.out.println("现在b的值是:"+b);}}}//现在y的值是:10现在b的值是:20例子3public class Example3_3{ public static void main(String args[]) { int a=9,b=5,c=7,t;if(a>b){ t=a; a=b; b=t;}if(a>c){ t=a; a=c; c=t;}if(b>c){ t=b; b=c; c=t;}System.out.println("a="+a+",b="+b+",c="+c);}}//a=5,b=7,c=9例子4public class Example3_4{ public static void main(String args[]) { int math=65 ,english=85;if(math>60){ System.out.println("数学及格了");}else{ System.out.println("数学不及格");}if(english>90){ System.out.println("英语是优");}else{ System.out.println("英语不是优");}System.out.println("我在学习控制语句");}}//数学及格了英语不是优我在学习控制语句例子5public class Example3_5{ public static void main(String args[]) { int x=2,y=1;switch(x+y){ case 1 :System.out.println(x+y);break;case 3:System.out.println(x+y);case 0:System.out.println(x+y);break;default: System.out.println("没有般配的"+(x+y));}}}例子6public class Example3_6{ public static void main(String args[]){ long sum=0,a=5,item=a,n=10,i=1;for(i=1;i<=n;i++){ sum=sum+item;item=item*10+a;}System.out.println(sum);}}例子7class Example3_7{ public static void main(String args[]){ double sum=0,a=1;int i=1;while(i<=20){ sum=sum+a;i=i+1;a=a*(1.0/i);}System.out.println("sum="+sum);}}例子8class Example3_8{ public static void main(String args[]){ int sum=0,i,j;for( i=1;i<=10;i++){ if(i%2==0) //计算1+3+5+7+9continue;sum=sum+i;}System.out.println("sum="+sum);for(j=2;j<=50;j++) //求50以内的素数{ for( i=2;i<=j/2;i++){ if(j%i==0)break;}if(i>j/2){ System.out.println(""+j+"是素数"); }}}}第一章字符串例子1class 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));System.out.println(s1==s2);String s3,s4;s3="how are you";s4="how are you";System.out.println(s3.equals(s4));System.out.println(s3==s4);}}//结果：true,false,true,true例子2判断一个字符串中出现了几个enclass 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);}}//结果：number=5例子3class Example5_3{ public static void main(String args[]){ String a[]={"door","apple","Applet","girl","boy"};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]);}}}结果： Applet apple boy door girl例子4class Example5_4{ public static void main(String args[]){ String path="c:\\myfile\\2000\\result.txt";int index=stIndexOf("\\");String fileName=path.substring(index+1);String newName=fileName.replaceAll(".txt",".java");System.out.println(path);System.out.println(fileName);System.out.println(newName);}}结果：c:\myfile\2000\result.txtResult.txtResult.java例子5public class Example5_5{ public static void main(String args[]){ double n,sum=0,item=0;boolean computable=true;for(int i=0;i<args.length;i++){ try{ item=Double.parseDouble(args[i]);sum=sum+item;}catch(NumberFormatException e){ System.out.println("您键入了非数字字符:"+e);computable=false;}}if(computable){ n=sum/args.length;System.out.println("平均数:"+n);}结果：输入数字不同，结果不同int number=123456;String binaryString=Long.toBinaryString(number);System.out.println(number+"的二进制表示:"+binaryString);System.out.println(number+"的十六进制表示:"+Long.toString(number,16));String str="1110110";int p=0,m=0;for(int i=str.length()-1;i>=0;i--){ char c=str.charAt(i);int a=Integer.parseInt(""+c);p=p+(int)(a*Math.pow(2,m));m++;}System.out.println(str+"的十进制表示:"+p);}}结果：123456的二进制表示：11110001001000000123456的十六进制表示：1e2401110110的十进制表示：118例子6import java.util.Date;import java.awt.*;public class Example5_6{ public static void main(String args[]){ Date date=new Date();Button button=new Button("确定");System.out.println(date.toString());System.out.println(button.toString());}}结果：Tue Sep 11 23:55:03 CST 2007java.awt.Button[button0,0,0,0x0,invalid,label=确定] 运行时间不同，结果不同例子7import java.util.*;public class Example5_7{ public static void main(String args[]){ String s="I am Geng.X.y,she is my girlfriend";StringTokenizer fenxi=new StringTokenizer(s," ,");int number=fenxi.countTokens();while(fenxi.hasMoreTokens()){ String str=fenxi.nextToken();System.out.println(str);System.out.println("还剩"+fenxi.countTokens()+"个单词");}System.out.println("s共有单词："+number+"个");}}例子8class Example5_8{ public static void main(String args[]){ char c[],d[];String s="巴西足球队击败德国足球队";c=new char[2];s.getChars(5,7,c,0);System.out.println(c);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9class Example5_9{ public static void main(String args[]){ String s="清华大学出版社";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10public class Example5_10{ public static void main(String args[]){ byte d[]="你我他".getBytes();System.out.println("数组d的长度是(一个汉字占两个字节):"+d.length);String s=new String(d,0,2);System.out.println(s);}}例子11class Example5_11{ public static void main(String args[ ]){ StringBuffer str=new StringBuffer("62791720");str.insert(0,"010-");str.setCharAt(7 ,'8');str.setCharAt(str.length()-1,'7');System.out.println(str);str.append("-446");System.out.println(str);str.reverse();System.out.println(str);}}例子12public class Example5_12{ public static void main (String args[ ]){String regex="\\w{1,}@\\w{1,}\56\\w{1,}" ;String str1="zhangsan@";String str2="li@si@";if(str1.matches(regex)){ System.out.println(str1+"是一个Email地址");}else{ System.out.println(str1+"不是一个Email地址");}if(str2.matches(regex)){ System.out.println(str2+"是一个Email地址");}else{ System.out.println(str2+"不是一个Email地址");}}}。