package cyy;
public class cl {public static void main(String[] args) {String  s1="Hello!";String s2="World";String s3=s1+s2;s3=s2.concat(s1);System.out.println(s3);}}

package cyy;
public class cl {public static void main(String[] args) {StringBuilder s1=new StringBuilder("Hello!");StringBuilder s2=new StringBuilder("World");StringBuilder builder=new StringBuilder();builder.append(s1);builder.append(s2);System.out.println(builder);}
}

public class Message
{
public static void main(String[] args){     if (args[0].equals(“-h”)) System.out.print(“Hello”);else if(args[0].equals(“-g”)) System.out.print(“goodbye,”);for(int i=1;i<args.length;i++)System.out.print(“  ”+args[i]);System.out.println(“!”);}
}

import java.util.*;/*** This program demonstrates a <code>while</code> loop.* @version 1.20 2004-02-10* @author Cay Horstmann*/
public class Retirement
{public static void main(String[] args){// read inputsScanner in = new Scanner(System.in);   //通过控制台进行输入时，需要构建一个Scanner对象，并与“标准输入流”System.in关联。System.out.print("How much money do you need to retire? "); double goal = in.nextDouble();//输入"How much money do you need to retire? "的内容；System.out.print("How much money will you contribute every year? ");double payment = in.nextDouble();//输入"How much money will you contribute every year? "的内容；System.out.print("Interest rate in %: ");double interestRate = in.nextDouble();//输入"Interest rate in %: "的内容；double balance = 0; //定义双精度型 balance，并进行初始化；int years = 0;      //定义整型years，并进行初始化；// update account balance while goal isn't reachedwhile (balance < goal)                   //while循环{// add this year's payment and interestbalance += payment;                   //balance=balance + payment；double interest = balance * interestRate / 100;balance += interest;years++;}System.out.println("You can retire in " + years + " years.");}
}

import java.util.*;/*** This program demonstrates a <code>do/while</code> loop.* @version 1.20 2004-02-10* @author Cay Horstmann*/
public class Retirement2
{public static void main(String[] args){Scanner in = new Scanner(System.in);   //通过控制台进行输入时，需要构建一个Scanner对象，并与“标准输入流”System.in关联。System.out.print("How much money will you contribute every year? ");double payment = in.nextDouble();       //输入"How much money will you contribute every year? "的内容；System.out.print("Interest rate in %: ");double interestRate = in.nextDouble();  //输入"Interest rate in %: "的内容；double balance = 0;int year = 0;String input;// update account balance while user isn't ready to retiredo                                    //do-while循环{// add this year's payment and interestbalance += payment;                 //balance=balance+payment；double interest = balance * interestRate / 100;balance += interest;year++;// print current balanceSystem.out.printf("After year %d, your balance is %,.2f%n", year, balance);// ask if ready to retire and get inputSystem.out.print("Ready to retire? (Y/N) ");input = in.next();}while (input.equals("N"));  //循环满足的条件，当输入“Y”的时候结束循环语句；}
}

import java.util.*;/*** This program demonstrates a <code>for</code> loop.* @version 1.20 2004-02-10* @author Cay Horstmann*/
public class LotteryOdds
{public static void main(String[] args){Scanner in = new Scanner(System.in);System.out.print("How many numbers do you need to draw? ");int k = in.nextInt();   //输入"How many numbers do you need to draw? "的内容；System.out.print("What is the highest number you can draw? ");int n = in.nextInt();  //输入"What is the highest number you can draw? "的内容；/** compute binomial coefficient n*(n-1)*(n-2)*...*(n-k+1)/(1*2*3*...*k)*/int lotteryOdds = 1;for (int i = 1; i <= k; i++)    //for循环；lotteryOdds = lotteryOdds * (n - i + 1) / i;System.out.println("Your odds are 1 in " + lotteryOdds + ". Good luck!");}
}