（1）随机数
取余的m很大可以保证随机的更彻底，更不容易重复
1 import java.util.Scanner; 2 public class Text_001 3 { 4 5 public static void main(String[] args) 6 { 7 Scanner input=new Scanner(System.in); 8 int x1;//x[n-1] 9 int x2;//x[n] 10 int a=16807;//Multiplier=75=16807 11 int c=0; 12 int m=2001;//Modulus=2^31-1=int.MaxValue 当显示过231-2个数之后，才可能重复 13 int n=0; 14 int num=1000;//数量 15 System.out.println("请输入数量"); 16 num=input.nextInt(); 17 for(n=1,x1=a;n<=num;n++) 18 { 19 x2=(a*x1+c)%m; 20 System.out.print(x2+"\t"); 21 if(n%5==0)System.out.println(); 22 x1=x2; 23 } 24 } 25 }
(2)
课件代码示例
1 // MethodOverload.java 2 // Using overloaded methods 3 4 public class MethodOverload { 5 6 public static void main(String[] args) { 7 System.out.println("The square of integer 7 is " + square(7)); 8 System.out.println("\nThe square of double 7.5 is " + square(7.5)); 9 } 10 11 public static int square(int x) { 12 return x * x; 13 } 14 15 public static double square(double y) { 16 return y * y; 17 } 18 }
println是一个方法，参数数量可变
原因……看了看api，找到了一下两行，很明显有省略号
PrintStream |
printf(Locale l, String format, Object... args)
A convenience method to write a formatted string to this output stream using the specified format string and arguments.
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PrintStream |
printf(String format, Object... args)
A convenience method to write a formatted string to this output stream using the specified format string and arguments.
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（3）输出素数
1 import java.util.ArrayList; 2 import java.util.Scanner; 3 public class Sushu 4 { 5 6 public static void main(String[] args) 7 { 8 ArrayList<Integer> num=new ArrayList<Integer>(); 9 Scanner input=new Scanner(System.in); 10 int min=3,max=100; 11 System.out.println("请输入两个整数"); 12 min=input.nextInt(); 13 max=input.nextInt(); 14 num=Judge(min, max); 15 show(num); 16 } 17 public static void show(ArrayList<Integer> num) 18 { 19 int k=0,i=0; 20 //所有 21 System.out.println("遍历"); 22 for(i=0;i<num.size();i++) 23 { 24 System.out.print(num.get(i)+"\t"); 25 k++; 26 if(k==5) 27 { 28 k=0; 29 System.out.println(); 30 } 31 } 32 //最大 33 System.out.println("\n最大"); 34 for(i=0,k=0;i<10&&i<num.size()&&num.size()-i>=0;i++) 35 { 36 System.out.print(num.get(num.size()-i-1)+"\t"); 37 k++; 38 if(k==5) 39 { 40 k=0; 41 System.out.println(); 42 } 43 } 44 //最小 45 System.out.println("\n最小"); 46 for(i=0,k=0;i<10&&i<num.size();i++) 47 { 48 System.out.print(num.get(i)+"\t"); 49 k++; 50 if(k==5) 51 { 52 k=0; 53 System.out.println(); 54 } 55 } 56 } 57 public static ArrayList<Integer> Judge(int min,int max) 58 { 59 int i=0,t=0,n=0,f=0; 60 ArrayList<Integer> num=new ArrayList<Integer>(); 61 for(i=min;i<=max;i++) 62 { 63 n=(int)(Math.sqrt((double)i)); 64 for(t=2,f=0;t<=n;t++) 65 { 66 if(i%t==0) 67 { 68 f=1; 69 break; 70 } 71 } 72 if(f==0)num.add(i); 73 } 74 return num; 75 } 76 }
(4)使用递归，判断是否为回文
就像剥洋葱一样，一层层往下剥。最后剩下一个，或一个不剩，说明是回文
1 import java.util.Scanner; 2 public class Palindrome 3 { 4 5 public static void main(String[] args) 6 { 7 Scanner input=new Scanner(System.in); 8 String s="我是谁是我"; 9 String t=""; 10 System.out.println("请输入一个句子"); 11 s=input.nextLine(); 12 t=fun(s); 13 if(t.length()<=1) 14 { 15 System.out.println(s+" 是回文"); 16 } 17 else 18 { 19 System.out.println("不是回文"); 20 } 21 } 22 public static String fun(String s) 23 { 24 if(s.length()>1&&s.charAt(0)==s.charAt(s.length()-1)) 25 { 26 s=s.substring(1, s.length()-1); 27 return fun(s); 28 } 29 else 30 { 31 return s; 32 } 33 } 34 }
（5）统计一篇英语问斩单词出现频率（从文件中读取）
一个一个字符分析，如果出现字母，再次出现不是字母的，那么值钱的字母记为一个单词，存到字符串内
1 import java.util.ArrayList; 2 import java.util.Scanner; 3 4 import java.io.*; 5 6 public class StatisticsWord 7 { 8 public static void main(String[] args) 9 { 10 String fileName="e1.txt",fileName2="e4.txt"; 11 String line=""; 12 String word=""; 13 int p=0; 14 int lineLength=0; 15 int f1=0,f2=0; 16 int sum=10; 17 char c; 18 Scanner input=new Scanner(System.in); 19 ArrayList<String> wordRecoed=new ArrayList<String>(); 20 ArrayList<Integer> wordNum=new ArrayList<Integer>(); 21 System.out.println("请输入读取的文件名"); 22 fileName=input.nextLine(); 23 System.out.println("请输入用于储存的文件名"); 24 fileName2=input.nextLine(); 25 System.out.println("请输入数量"); 26 sum=input.nextInt(); 27 try 28 { 29 FileReader fr=new FileReader(fileName); 30 Scanner in=new Scanner(fr); 31 //读取 32 while(in.hasNextLine()) 33 { 34 line=line+in.nextLine()+"\n"; 35 } 36 in.close(); 37 fr.close(); 38 lineLength=line.length(); 39 //System.out.println(line+" "+lineLength); 40 while(p<lineLength) 41 { 42 f1=0; 43 f2=0; 44 word=""; 45 //拆分 46 do 47 { 48 c=line.charAt(p++); 49 //System.out.print(c+" | "); 50 if(c==' '||c=='\n') 51 { 52 if(f1==1) 53 { 54 f2=1; 55 } 56 break; 57 } 58 else 59 { 60 if((c>='a'&&c<='z')||c>='A'&&c<='Z') 61 { 62 f1=1; 63 word=word+c; 64 } 65 else 66 { 67 if(f1==1) 68 { 69 f2=1; 70 } 71 break; 72 } 73 } 74 75 }while(p<lineLength); 76 if(f2==1) 77 { 78 //对比 79 Compare(wordRecoed,wordNum,word); 80 } 81 } 82 //排序 83 Sort(wordRecoed, wordNum); 84 for(int x=0;x<sum;x++) 85 { 86 System.out.println(wordRecoed.get(x)+" "+wordNum.get(x)); 87 } 88 89 write(wordRecoed,wordNum,fileName2,sum); 90 } 91 catch(Exception e) 92 { 93 e.printStackTrace(); 94 } 95 96 } 97 public static void write(ArrayList<String> wordRecoed,ArrayList<Integer> wordNum,String s,int sum) 98 { 99 int i=0; 100 try 101 { 102 File f=new File(s); 103 if(!f.exists()) 104 { 105 f.createNewFile(); 106 } 107 FileWriter fr=new FileWriter(f); 108 PrintWriter pw=new PrintWriter(fr); 109 for(i=0;i<sum;i++) 110 { 111 pw.println(wordRecoed.get(i)+" "+wordNum.get(i)); 112 } 113 pw.flush(); 114 pw.close(); 115 fr.close(); 116 117 } 118 catch(Exception e) 119 { 120 e.printStackTrace(); 121 } 122 } 123 public static void Sort(ArrayList<String> wordRecoed,ArrayList<Integer> wordNum) 124 { 125 int l=wordRecoed.size();//长度 126 int i,t,k,j; 127 String s1,s2; 128 for(i=0;i<l-1;i++) 129 { 130 for(t=0;t<l-i-1;t++) 131 { 132 if(wordNum.get(t)<=wordNum.get(t+1)) 133 { 134 //交换 135 k=wordNum.get(t); 136 j=wordNum.get(t+1); 137 wordNum.set(t+1, k); 138 wordNum.set(t, j); 139 s1=wordRecoed.get(t); 140 s2=wordRecoed.get(t+1); 141 wordRecoed.set(t+1, s1); 142 wordRecoed.set(t, s2); 143 } 144 } 145 } 146 } 147 public static void Compare(ArrayList<String> wordRecoed,ArrayList<Integer> wordNum,String word) 148 { 149 int l=wordRecoed.size();//长度 150 int i=0,t=0; 151 int flag1=0; 152 for(i=0;i<l;i++) 153 { 154 if(wordRecoed.get(i).equals(word)) 155 { 156 t=wordNum.get(i)+1; 157 wordNum.set(i, t); 158 flag1=1; 159 break; 160 } 161 } 162 if(l==0||flag1==0) 163 { 164 wordRecoed.add(word); 165 wordNum.add(1); 166 } 167 } 168 }