String s1=“Hello!”;String s2=“World”;String s3=s1+s2;

 1 package MyProject;
 2
 3 public class Week2 {
 4
 5     public static void main(String[] args)
 6     {
 7         // TODO Auto-generated method stub
 8         String s1 ="Hello!";
 9         String s2= "World";
10         String s3=s1+s2;
11         System.out.println(s3);
12     }
13
14 }

 1 package MyProject;
 2
 3 public class Week2{
 4     public static void main(String[] args)
 5 {
 6     StringBuilder s1=new StringBuilder("Hello!");
 7     StringBuilder s2=new StringBuilder("world");
 8     StringBuilder s3=new StringBuilder();
 9     s3.append(s1);   //append 字符拼接
10     System.out.println(s3);
11  }
12 }

 1 package MyProject;
 2
 3         public class Message
 4         {
 5         public static void main(String[] args)
 6           {
 7           if (args[0].equals("-h")) System.out.print("Hello");
 8             else if(args[0].equals("-g")) System.out.print("goodbye,");
 9           for(int i=1;i<args.length;i++)
10             System.out.print("  "+args[i]);
11           System.out.println("!");
12           }
13
14     }

 1 import java.util.*;
 2
 3 /**
 4  * This program demonstrates console input.
 5  * @version 1.10 2004-02-10
 6  * @author Cay Horstmann
 7  */
 8 public class InputTest
 9 {
10    public static void main(String[] args)
11    {
12       Scanner in = new Scanner(System.in);
13
14       // get first input
15       System.out.print("What is your name? ");
16       String name = in.nextLine();
17
18       // get second input
19       System.out.print("How old are you? ");
20       int age = in.nextInt();
21
22       // display output on console
23       System.out.println("Hello, " + name + ". Next year, you'll be " + (age + 1));
24    }
25 }

 1 import java.io.File;
 2 import java.io.FileNotFoundException;
 3 import java.io.PrintWriter;
 4 import java.util.Scanner;
 5 import java.util.Arrays;
 6
 7 public class WriteReadFileTest {
 8
 9     /**
10      * @param args
11      * @throws FileNotFoundException
12      */
13     public static void main(String[] args) throws FileNotFoundException {
14
15         //写入文件演示
16         PrintWriter out = new PrintWriter("myfile.txt");
17         out.println("姓名 高数 Java 数据结构 平均成绩 总成绩");
18         out.println("张三 20 30 40 0 0");
19         out.println("李四 50 60 70 0 0");
20         out.close();//切记，输出完毕，需要close
21
22
23         //读入文件演示
24         Scanner in = new Scanner(new File("myfile.txt"));//为myfile.txt这个File创建一个扫描器in
25         int number = 1;//行号
26         while(in.hasNextLine()){//判断扫描器是否还有下一行未读取，该循环把文件的每一行都读出
27             String line = in.nextLine();//读出myfile.txt的下一行
28             System.out.println("第"+(number++)+"行的内容" +"="+line);
29
30             Scanner linescanner = new Scanner(line);//对每一行的内容建立一个扫描器
31             linescanner.useDelimiter(" ");//使用空格作为分隔符
32             String name = linescanner.next();
33             String math = linescanner.next();
34             String java = linescanner.next();
35             String ds = linescanner.next();
36             String avg = linescanner.next();
37             String total = linescanner.next();
38             System.out.println("name="+name+" math="+math+" java="+java+" ds="+ds+" avg"+avg+" total="+total);
39         }
40         in.close();//读入完毕，最后需要对其进行close。
41
42  }
43 }

 1 import java.util.*;
 2
 3 /**
 4  * This program demonstrates a <code>while</code> loop.
 5  * @version 1.20 2004-02-10
 6  * @author Cay Horstmann
 7  */
 8 public class Retirement
 9 {
10    public static void main(String[] args)
11    {
12       // read inputs
13       Scanner in = new Scanner(System.in);
14
15       System.out.print("How much money do you need to retire? ");
16       double goal = in.nextDouble();
17
18       System.out.print("How much money will you contribute every year? ");
19       double payment = in.nextDouble();
20
21       System.out.print("Interest rate in %: ");
22       double interestRate = in.nextDouble();
23
24       double balance = 0;
25       int years = 0;
26
27       // update account balance while goal isn't reached
28       while (balance < goal)
29       {
30          // add this year's payment and interest
31          balance += payment;
32          double interest = balance * interestRate / 100;
33          balance += interest;
34          years++;
35       }
36
37       System.out.println("You can retire in " + years + " years.");
38    }
39 }

 1 import java.util.*;
 2
 3 /**
 4  * This program demonstrates a <code>do/while</code> loop.
 5  * @version 1.20 2004-02-10
 6  * @author Cay Horstmann
 7  */
 8 public class Retirement2
 9 {
10    public static void main(String[] args)
11    {
12       Scanner in = new Scanner(System.in);
13
14       System.out.print("How much money will you contribute every year? ");
15       double payment = in.nextDouble();
16
17       System.out.print("Interest rate in %: ");
18       double interestRate = in.nextDouble();
19
20       double balance = 0;
21       int year = 0;
22
23       String input;
24
25       // update account balance while user isn't ready to retire
26       do
27       {
28          // add this year's payment and interest
29          balance += payment;
30          double interest = balance * interestRate / 100;
31          balance += interest;
32
33          year++;
34
35          // print current balance
36          System.out.printf("After year %d, your balance is %,.2f%n", year, balance);
37
38          // ask if ready to retire and get input
39          System.out.print("Ready to retire? (Y/N) ");
40          input = in.next();
41       }
42       while (input.equals("N"));
43    }
44 }

 1 import java.util.*;
 2
 3 /**
 4  * This program demonstrates a <code>for</code> loop.
 5  * @version 1.20 2004-02-10
 6  * @author Cay Horstmann
 7  */
 8 public class LotteryOdds
 9 {
10    public static void main(String[] args)
11    {
12       Scanner in = new Scanner(System.in);
13
14       System.out.print("How many numbers do you need to draw? ");
15       int k = in.nextInt();
16
17       System.out.print("What is the highest number you can draw? ");
18       int n = in.nextInt();
19
20       /*
21        * compute binomial coefficient n*(n-1)*(n-2)*...*(n-k+1)/(1*2*3*...*k)
22        */
23
24       int lotteryOdds = 1;
25       for (int i = 1; i <= k; i++)
26          lotteryOdds = lotteryOdds * (n - i + 1) / i;
27
28       System.out.println("Your odds are 1 in " + lotteryOdds + ". Good luck!");
29    }
30 }