程序代码：

Java 代码规范
一：缩进
代码1：不良的风格
public class Welcome
{
public static void main(String[] args)
{
String[] greeting = new String[3];
greeting[0] = "Welcome to Core Java";
greeting[1] = "by Cay Horstmann";
greeting[2] = "and Gary Cornell";

for (String g : greeting)
System.out.println(g);
}
}

代码2：良好的风格
public class Welcome
{
   public static void main(String[] args)
   {
      String[] greeting = new String[3];
      greeting[0] = "Welcome to Core Java";
      greeting[1] = "by Cay Horstmann";
      greeting[2] = "and Gary Cornell";

      for (String g : greeting)
         System.out.println(g);
   }
}

评： 代码1结构混乱，代码2结构清析

二：空格
代码1：不良的风格
public class Retirement
{
   public static void main(String[] args)
   {
      // read inputs
      Scanner in=new Scanner(System.in);

      System.out.print("How much money do you need to retire? ");
      double goal=in.nextDouble();

      System.out.print("How much money will you contribute every year? ");
      double payment = in.nextDouble();

      System.out.print("Interest rate in %: ");
      double interestRate=in.nextDouble();

      double balance=0;
      int years=0;

      // update account balance while goal isn't reached
      while (balance<goal)
      {
         // add this year's payment and interest
         balance+=payment;
         double interes=balance*interestRate/100;
         balance+=interest;
         years++;
      }

      System.out.println("You can retire in " + years + " years.");
   }
}

代码2：良好的风格
public class Retirement
{
   public static void main(String[] args)
   {
      // read inputs
      Scanner in = new Scanner(System.in);

      System.out.print("How much money do you need to retire? ");
      double goal = in.nextDouble();

      System.out.print("How much money will you contribute every year? ");
      double payment = in.nextDouble();

      System.out.print("Interest rate in %: ");
      double interestRate = in.nextDouble();

      double balance = 0;
      int years = 0;

      // update account balance while goal isn't reached
      while (balance < goal)
      {
         // add this year's payment and interest
         balance += payment;
         double interest = balance * interestRate / 100;
         balance += interest;
         years++;
      }

      System.out.println("You can retire in " + years + " years.");
   }
}

评：代码1运算符前后没有打上空格，代码挤压，不美观

三：语句
代码1：不良的风格
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);

      System.out.print("How much money will you contribute every year? ");
      double payment = in.nextDouble();

      System.out.print("Interest rate in %: ");
      double interestRate = in.nextDouble();double balance = 0;int year = 0;

      String input;

      // update account balance while user isn't ready to retire
      do
      {
         // add this year's payment and interest
         balance += payment;double interest = balance * interestRate / 100;balance += interest;


 year++;

         // print current balance
         System.out.printf("After year %d, your balance is %,.2f%n", year, balance);

         // ask if ready to retire and get input
         System.out.print("Ready to retire? (Y/N) ");
         input = in.next();
      }
      while (input.equals("N"));
   }
}

代码2：良好的风格
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);

      System.out.print("How much money will you contribute every year? ");
      double payment = in.nextDouble();

      System.out.print("Interest rate in %: ");
      double interestRate = in.nextDouble();

      double balance = 0;
      int year = 0;

      String input;

      // update account balance while user isn't ready to retire
      do
      {
         // add this year's payment and interest
         balance += payment;
         double interest = balance * interestRate / 100;
         balance += interest;

         year++;

         // print current balance
         System.out.printf("After year %d, your balance is %,.2f%n", year, balance);

         // ask if ready to retire and get input
         System.out.print("Ready to retire? (Y/N) ");
         input = in.next();
      }
      while (input.equals("N"));
   }
}
评：应该遵循一条语句一行代码，代码2显然要比代码1清析美观

四：自增运算符
代码1：不良的风格
public class Hello
{
   public static void main(String[] args)
   {
      int i, j;
      j = i++ + i++ + i++;
   }
}
评：不要在一对顺序点之间改变同一个变量两次，会给人迷惑的感觉，并且还会带来烦人的bug

五：循环计数器
代码1：不良的风格
public class LotteryArray
{
   public static void main(String[] args)
   {
      final int NMAX = 10;
      int i, j, k;
      // allocate triangular array
      int[][] odds = new int[NMAX + 1][];
      for ( i = 0; i <= NMAX; i++)
         odds[i] = new int[i + 1];

      // fill triangular array
      for ( i = 0; i < odds.length; i++)
         for ( j = 0; j < odds[i].length; j++)
         {
            /*
             * compute binomial coefficient n*(n-1)*(n-2)*...*(n-k+1)/(1*2*3*...*k)
             */
            int lotteryOdds = 1;
            for ( i = 1; i <= j; i++)
               lotteryOdds = lotteryOdds * (n - i + 1) / i;

            odds[i][j] = lotteryOdds;
         }

      // print triangular array
      for (int[] row : odds)
      {
         for (int odd : row)
            System.out.printf("%4d", odd);
         System.out.println();
      }
   }
}

代码2：良好的风格
/**

 * This program demonstrates a triangular array.

 * @version 1.20 2004-02-10

 * @author Cay Horstmann

 */
public class LotteryArray
{
   public static void main(String[] args)
   {
      final int NMAX = 10;

      // allocate triangular array
      int[][] odds = new int[NMAX + 1][];
      for (int n = 0; n <= NMAX; n++)
         odds[n] = new int[n + 1];

      // fill triangular array
      for (int n = 0; n < odds.length; n++)
         for (int k = 0; k < odds[n].length; k++)
         {
            /*
             * 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++)
               lotteryOdds = lotteryOdds * (n - i + 1) / i;

            odds[n][k] = lotteryOdds;
         }

      // print triangular array
      for (int[] row : odds)
      {
         for (int odd : row)
            System.out.printf("%4d", odd);
         System.out.println();
      }
   }
}
评：代码1中定义了 3个临时变量 i, j, k。却只用了 i, j.
多出来的 k 难免让人有点模不着头脑的感觉

六：变量命名
代码1：不良的风格
class Employee
{
   public Employee(String n, double s, int year, int month, int day)
   {
      n = n;
      s = s;
      GregorianCalendar calendar = new GregorianCalendar(year, month - 1, day);
      // GregorianCalendar uses 0 for January
      d = calendar.getTime();
   }

   public String getN()
   {
      return n;
   }

   public double getS()
   {
      return s;
   }

   public Date getD()
   {
      return d;
   }

   public void raiseS(double byPercent)
   {
      double raise = s * byPercent / 100;
      s += raise;
   }

   private String n;
   private double s;
   private Date d;
}

代码2：良好的风格
class Employee
{
   public Employee(String n, double s, int year, int month, int day)
   {
      name = n;
      salary = s;
      GregorianCalendar calendar = new GregorianCalendar(year, month - 1, day);
      // GregorianCalendar uses 0 for January
      hireDay = calendar.getTime();
   }

   public String getName()
   {
      return name;
   }

   public double getSalary()
   {
      return salary;
   }

   public Date getHireDay()
   {
      return hireDay;
   }

   public void raiseSalary(double byPercent)
   {
      double raise = salary * byPercent / 100;
      salary += raise;
   }

   private String name;
   private double salary;
   private Date hireDay;
}
评：变量命名应该简短，富于描述。能让人见名知义

七：常量命名
代码1：不良的风格
public class CompoundInterest
{
   public static void main(String[] args)
   {
      final double Startrate = 10;
      final int Nrates = 6;
      final int Nyears = 10;

      // set interest rates to 10 . . . 15%
      double[] interestRate = new double[Nrates];
      for (int j = 0; j < interestRate.length; j++)
         interestRate[j] = (Startrate + j) / 100.0;

      double[][] balances = new double[Nyears][Nrates];

      // set initial balances to 10000
      for (int j = 0; j < balances[0].length; j++)
         balances[0][j] = 10000;

      // compute interest for future years
      for (int i = 1; i < balances.length; i++)
      {
         for (int j = 0; j < balances[i].length; j++)
         {
            // get last year's balances from previous row
            double oldBalance = balances[i - 1][j];

            // compute interest
            double interest = oldBalance * interestRate[j];

            // compute this year's balances
            balances[i][j] = oldBalance + interest;
         }
      }

      // print one row of interest rates
      for (int j = 0; j < interestRate.length; j++)
         System.out.printf("%9.0f%%", 100 * interestRate[j]);

      System.out.println();

      // print balance table
      for (double[] row : balances)
      {
         // print table row
         for (double b : row)
            System.out.printf("%10.2f", b);

         System.out.println();
      }
   }
}

代码2：良好的风格
public class CompoundInterest
{
   public static void main(String[] args)
   {
      final double STARTRATE = 10;
      final int NRATES = 6;
      final int NYEARS = 10;

      // set interest rates to 10 . . . 15%
      double[] interestRate = new double[NRATES];
      for (int j = 0; j < interestRate.length; j++)
         interestRate[j] = (STARTRATE + j) / 100.0;

      double[][] balances = new double[NYEARS][NRATES];

      // set initial balances to 10000
      for (int j = 0; j < balances[0].length; j++)
         balances[0][j] = 10000;

      // compute interest for future years
      for (int i = 1; i < balances.length; i++)
      {
         for (int j = 0; j < balances[i].length; j++)
         {
            // get last year's balances from previous row
            double oldBalance = balances[i - 1][j];

            // compute interest
            double interest = oldBalance * interestRate[j];

            // compute this year's balances
            balances[i][j] = oldBalance + interest;
         }
      }

      // print one row of interest rates
      for (int j = 0; j < interestRate.length; j++)
         System.out.printf("%9.0f%%", 100 * interestRate[j]);

      System.out.println();

      // print balance table
      for (double[] row : balances)
      {
         // print table row
         for (double b : row)
            System.out.printf("%10.2f", b);

         System.out.println();
      }
   }
}

评：常量名应该全部大写，不然给人感觉很怪异

八：case 标签
代码1：不良的风格
switch(key)
{      
       case  1:
           direction = key;
           break;
       case 2:            
           direction = key;
           break;      
       case 3:
           direction = key;
           break;
       case 4：
:   direction = key;
           break;
}

代码2：良好的风格
switch(key)
{      
       case  LEFT:
           direction = key;
           break;
       case RIGHT:            
           direction = key;
           break;      
       case UP:
           direction = key;
           break;
       case DOWN：
:   direction = key;
           break;
}
评：代码中尽量不要出现数字，否则不去阅读代码根本不知道这个数字代表的意思。
最好用符号常量代替。

九：多重选择
代码1：不良的风格
if (key == LEFT)
   direction = key;
else if (key == RIGHT)
   direction = key;
else if (key == UP )
   direction = key;
else if (key == DOWN)
   direction = key;

代码2：良好的风格
switch(key)
{      
       case  LEFT:
           direction = key;
           break;
       case RIGHT:            
           direction = key;
           break;      
       case UP:
           direction = key;
           break;
       case DOWN：
:   direction = key;
           break;
}

评：多于3个以上的分支结构最好不要使用 if/else, 晦涩难懂，尽量 使用 switch/case代替

十：中断流程
代码1：不良的风格
for( i = 0; aResult[i]==0 && i<resultPointPos; i++ ) ；

代码2：良好的风格
for( i = 0; aResult[i]==0 && i<resultPointPos; i++ )
            continue;
评：循环结构中的 空语句尽量不用使用 ；，用continue 代替，代码易读，而且不易出错。