【转】Java与C#语言级比较

原文链接：http://www.harding.edu/fmccown/java_csharp_comparison.html

Java

程序结构

C#

package hello;
public class HelloWorld {    public static void main(String[] args) {       String name = "Java";
      // See if an argument was passed from the command line       if (args.length == 1)          name = args[0];
      System.out.println("Hello, " + name + "!");     } }

using System; 
namespace Hello {    public class HelloWorld {       public static void Main(string[] args) {          string name = "C#";
         // See if an argument was passed from the command line          if (args.Length == 1)             name = args[0];
         Console.WriteLine("Hello, " + name + "!");       }    } }

Java

注释

C#

// Single line /* Multiple     line  */ /** Javadoc documentation comments */

// Single line /* Multiple     line  */ /// XML comments on a single line /** XML comments on multiple lines */

Java

数据类型

C#

Primitive Types boolean byte char short, int, long float, double

Reference Types Object   (superclass of all other classes) String arrays, classes, interfaces

Conversions

// int to String  int x = 123;  String y = Integer.toString(x);  // y is "123"

// String to int y = "456";  x = Integer.parseInt(y);   // x is 456

// double to int double z = 3.5;  x = (int) z;   // x is 3  (truncates decimal)

Value Types bool byte, sbyte char short, ushort, int, uint, long, ulong float, double, decimal structures, enumerations

Reference Types object    (superclass of all other classes) string arrays, classes, interfaces, delegates

Convertions

// int to string  int x = 123;  String y = x.ToString();  // y is "123"

// string to int y = "456";  x = int.Parse(y);   // or x = Convert.ToInt32(y);

// double to int double z = 3.5;  x = (int) z;   // x is 3  (truncates decimal)

Java

常量

C#

// May be initialized in a constructor  final double PI = 3.14;

const double PI = 3.14;

// Can be set to a const or a variable. May be initialized in a constructor.  readonly int MAX_HEIGHT = 9;

Java

枚举

C#

enum Action {Start, Stop, Rewind, Forward};

// Special type of class  enum Status {   Flunk(50), Pass(70), Excel(90);   private final int value;   Status(int value) { this.value = value; }   public int value() { return value; }  };

Action a = Action.Stop; if (a != Action.Start)   System.out.println(a);               // Prints "Stop"
Status s = Status.Pass; System.out.println(s.value());      // Prints "70"

enum Action {Start, Stop, Rewind, Forward};

enum Status {Flunk = 50, Pass = 70, Excel = 90};

No equivalent.

Action a = Action.Stop; if (a != Action.Start)   Console.WriteLine(a);             // Prints "Stop"

Status s = Status.Pass; Console.WriteLine((int) s);       // Prints "70"

Java

操作符

C#

Comparison ==  <  >  <=  >=  !=

Arithmetic +  -  *  / %  (mod) /   (integer division if both operands are ints) Math.Pow(x, y)

Assignment =  +=  -=  *=  /=   %=   &=  |=  ^=  <<=  >>=  >>>=  ++  --

Bitwise &  |  ^   ~  <<  >>  >>>

Logical &&  ||  &  |   ^   !

Note: && and || perform short-circuit logical evaluations

String Concatenation +

Comparison ==  <  >  <=  >=  !=

Arithmetic +  -  *  / %  (mod) /   (integer division if both operands are ints) Math.Pow(x, y)

Assignment =  +=  -=  *=  /=   %=  &=  |=  ^=  <<=  >>=  ++  --

Bitwise &  |  ^   ~  <<  >>

Logical &&  ||  &  |   ^   !

Note: && and || perform short-circuit logical evaluations

String Concatenation +

Java

分支语句

C#

greeting = age < 20 ? "What's up?" : "Hello";

if (x < y)    System.out.println("greater");

if (x != 100) {       x *= 5;    y *= 2;  }  else    z *= 6;

int selection = 2; switch (selection) {     // Must be byte, short, int, char, or enum   case 1: x++;            // Falls through to next case if no break   case 2: y++;   break;    case 3: z++;   break;    default: other++; }

greeting = age < 20 ? "What's up?" : "Hello";

if (x < y)     Console.WriteLine("greater");

if (x != 100) {       x *= 5;    y *= 2;  }  else    z *= 6;
string color = "red"; switch (color) {                          // Can be any predefined type   case "red":    r++;    break;       // break is mandatory; no fall-through   case "blue":   b++;   break;    case "green": g++;   break;    default: other++;     break;       // break necessary on default }

Java

循环语句

C#

while (i < 10)    i++;
for (i = 2; i <= 10; i += 2)    System.out.println(i);

do    i++;  while (i < 10);

for (int i : numArray)  // foreach construct     sum += i;

// for loop can be used to iterate through any Collection import java.util.ArrayList; ArrayList<Object> list = new ArrayList<Object>(); list.add(10);    // boxing converts to instance of Integer list.add("Bisons"); list.add(2.3);    // boxing converts to instance of Double
for (Object o : list)   System.out.println(o);

while (i < 10)    i++;
for (i = 2; i <= 10; i += 2)    Console.WriteLine(i);

do    i++;  while (i < 10);

foreach (int i in numArray)     sum += i;

// foreach can be used to iterate through any collection  using System.Collections; ArrayList list = new ArrayList(); list.Add(10); list.Add("Bisons"); list.Add(2.3);
foreach (Object o in list)   Console.WriteLine(o);

Java

数组

C#

int nums[] = {1, 2, 3};   or   int[] nums = {1, 2, 3}; for (int i = 0; i < nums.length; i++)   System.out.println(nums[i]);
String names[] = new String[5]; names[0] = "David";
float twoD[][] = new float[rows][cols]; twoD[2][0] = 4.5;

int[][] jagged = new int[5][];  jagged[0] = new int[5];  jagged[1] = new int[2];  jagged[2] = new int[3];  jagged[0][4] = 5;

int[] nums = {1, 2, 3}; for (int i = 0; i < nums.Length; i++)   Console.WriteLine(nums[i]);
string[] names = new string[5]; names[0] = "David";
float[,] twoD = new float[rows, cols]; twoD[2,0] = 4.5f;

int[][] jagged = new int[3][] {     new int[5], new int[2], new int[3] };  jagged[0][4] = 5;

Java

方法

C#

// Return single value int Add(int x, int y) {     return x + y;  } int sum = Add(2, 3);

// Return no value void PrintSum(int x, int y) {     System.out.println(x + y);  } PrintSum(2, 3);

// Primitive types and references are always passed by value void TestFunc(int x, Point p) {    x++;     p.x++;       // Modifying property of the object    p = null;    // Remove local reference to object  }

class Point {     public int x, y;  }

Point p = new Point();  p.x = 2;  int a = 1;  TestFunc(a, p); System.out.println(a + " " + p.x + " " + (p == null) );  // 1 3 false

// Accept variable number of arguments int Sum(int ... nums) {   int sum = 0;   for (int i : nums)     sum += i;   return sum; }

int total = Sum(4, 3, 2, 1);   // returns 10

// Return single value int Add(int x, int y) {     return x + y;  } int sum = Add(2, 3);

// Return no value void PrintSum(int x, int y) {     Console.WriteLine(x + y);  } PrintSum(2, 3);

// Pass by value (default), in/out-reference (ref), and out-reference (out)  void TestFunc(int x, ref int y, out int z, Point p1, ref Point p2) {     x++;  y++;  z = 5;     p1.x++;       // Modifying property of the object          p1 = null;    // Remove local reference to object     p2 = null;   // Free the object  }

class Point {     public int x, y;  }

Point p1 = new Point();  Point p2 = new Point();  p1.x = 2;  int a = 1, b = 1, c;   // Output param doesn't need initializing  TestFunc(a, ref b, out c, p1, ref p2);  Console.WriteLine("{0} {1} {2} {3} {4}",     a, b, c, p1.x, p2 == null);   // 1 2 5 3 True

// Accept variable number of arguments int Sum(params int[] nums) {   int sum = 0;   foreach (int i in nums)     sum += i;   return sum; }

int total = Sum(4, 3, 2, 1);   // returns 10

Java

字符串

C#

// String concatenation String school = "Harding ";  school = school + "University";   // school is "Harding University"

// String comparison String mascot = "Bisons";  if (mascot == "Bisons")    // Not the correct way to do string comparisons if (mascot.equals("Bisons"))   // true if (mascot.equalsIgnoreCase("BISONS"))   // true if (mascot.compareTo("Bisons") == 0)   // true

System.out.println(mascot.substring(2, 5));   // Prints "son"

// My birthday: Oct 12, 1973 java.util.Calendar c = new java.util.GregorianCalendar(1973, 10, 12); String s = String.format("My birthday: %1$tb %1$te, %1$tY", c);

// Mutable string  StringBuffer buffer = new StringBuffer("two ");  buffer.append("three ");  buffer.insert(0, "one ");  buffer.replace(4, 7, "TWO");  System.out.println(buffer);     // Prints "one TWO three"

// String concatenation string school = "Harding ";  school = school + "University";   // school is "Harding University"

// String comparison string mascot = "Bisons";  if (mascot == "Bisons")    // true if (mascot.Equals("Bisons"))   // true if (mascot.ToUpper().Equals("BISONS"))   // true if (mascot.CompareTo("Bisons") == 0)    // true

Console.WriteLine(mascot.Substring(2, 3));    // Prints "son"

// My birthday: Oct 12, 1973 DateTime dt = new DateTime(1973, 10, 12); string s = "My birthday: " + dt.ToString("MMM dd, yyyy");

// Mutable string  System.Text.StringBuilder buffer = new System.Text.StringBuilder("two ");  buffer.Append("three ");  buffer.Insert(0, "one ");  buffer.Replace("two", "TWO");  Console.WriteLine(buffer);     // Prints "one TWO three"

Java

异常管理

C#

// Must be in a method that is declared to throw this exception Exception ex = new Exception("Something is really wrong.");  throw ex;

try {   y = 0;    x = 10 / y; } catch (Exception ex) {   System.out.println(ex.getMessage());  } finally {   // Code that always gets executed }

Exception up = new Exception("Something is really wrong.");  throw up;  // ha ha

try {   y = 0;    x = 10 / y; } catch (Exception ex) {      // Variable "ex" is optional   Console.WriteLine(ex.Message);  } finally {   // Code that always gets executed }

Java

命名空间

C#

package harding.compsci.graphics;

// Import single class import harding.compsci.graphics.Rectangle;

// Import all classes import harding.compsci.graphics.*;

namespace Harding.Compsci.Graphics {   ... }

or

namespace Harding {   namespace Compsci {     namespace Graphics {       ...     }   } }

// Import single class using Rectangle = Harding.CompSci.Graphics.Rectangle;

// Import all class using Harding.Compsci.Graphics;

Java

类和接口

C#

Accessibility keywords  public private protected static

// Inheritance class FootballGame extends Competition {   ... }

// Interface definition interface IAlarmClock {   ... }

// Extending an interface  interface IAlarmClock extends IClock {   ... }

// Interface implementation class WristWatch implements IAlarmClock, ITimer {    ... }

Accessibility keywords  public private internal protected protected internal static

// Inheritance class FootballGame : Competition {   ... }

// Interface definition interface IAlarmClock {   ... }

// Extending an interface  interface IAlarmClock : IClock {   ... }

// Interface implementation class WristWatch : IAlarmClock, ITimer {    ... }

Java

构造和析构

C#

class SuperHero {    private int mPowerLevel;

public SuperHero() {      mPowerLevel = 0;    }

public SuperHero(int powerLevel) {      this.mPowerLevel= powerLevel;    }

// No destructors, just override the finalize method   protected void finalize() throws Throwable {      super.finalize();   // Always call parent's finalizer      } }

class SuperHero {   private int mPowerLevel;
  public SuperHero() {      mPowerLevel = 0;   }
  public SuperHero(int powerLevel) {     this.mPowerLevel= powerLevel;    }
  ~SuperHero() {     // Destructor code to free unmanaged resources.     // Implicitly creates a Finalize method.   } }

Java

Objects

C#

SuperHero hero = new SuperHero();

hero.setName("SpamMan");  hero.setPowerLevel(3); 
hero.Defend("Laura Jones"); SuperHero.Rest();  // Calling static method

SuperHero hero2 = hero;   // Both refer to same object  hero2.setName("WormWoman");  System.out.println(hero.getName());  // Prints WormWoman 
hero = null;   // Free the object

if (hero == null)   hero = new SuperHero();

Object obj = new SuperHero();  System.out.println("object's type: " + obj.getClass().toString());  if (obj instanceof SuperHero)    System.out.println("Is a SuperHero object.");

SuperHero hero = new SuperHero(); 
hero.Name = "SpamMan";  hero.PowerLevel = 3;

hero.Defend("Laura Jones"); SuperHero.Rest();   // Calling static method

SuperHero hero2 = hero;   // Both refer to same object  hero2.Name = "WormWoman";  Console.WriteLine(hero.Name);   // Prints WormWoman

hero = null ;   // Free the object

if (hero == null)   hero = new SuperHero();

Object obj = new SuperHero();  Console.WriteLine("object's type: " + obj.GetType().ToString());  if (obj is SuperHero)    Console.WriteLine("Is a SuperHero object.");

Java

属性（获取器和设置器）

C#

private int mSize;

public int getSize() { return mSize; }  public void setSize(int value) {   if (value < 0)      mSize = 0;    else      mSize = value;  }

int s = shoe.getSize(); shoe.setSize(s+1);

private int mSize;

public int Size {    get { return mSize; }    set {      if (value < 0)        mSize = 0;      else        mSize = value;    }  }

shoe.Size++;

Java

结构类型

C#

No structs in Java.

struct StudentRecord {   public string name;   public float gpa;
  public StudentRecord(string name, float gpa) {     this.name = name;     this.gpa = gpa;   } }
StudentRecord stu = new StudentRecord("Bob", 3.5f); StudentRecord stu2 = stu;  
stu2.name = "Sue"; Console.WriteLine(stu.name);    // Prints "Bob" Console.WriteLine(stu2.name);   // Prints "Sue"

Java

控制台I/O

C#

java.io.DataInput in = new java.io.DataInputStream(System.in); System.out.print("What is your name? "); String name = in.readLine(); System.out.print("How old are you? "); int age = Integer.parseInt(in.readLine()); System.out.println(name + " is " + age + " years old.");

int c = System.in.read();   // Read single char System.out.println(c);      // Prints 65 if user enters "A"

// The studio costs $499.00 for 3 months. System.out.printf("The %s costs $%.2f for %d months.%n", "studio", 499.0, 3);

// Today is 06/25/04 System.out.printf("Today is %tD\n", new java.util.Date());

Console.Write("What's your name? "); string name = Console.ReadLine(); Console.Write("How old are you? "); int age = Convert.ToInt32(Console.ReadLine()); Console.WriteLine("{0} is {1} years old.", name, age); // or Console.WriteLine(name + " is " + age + " years old.");

int c = Console.Read();  // Read single char Console.WriteLine(c);    // Prints 65 if user enters "A"

// The studio costs $499.00 for 3 months. Console.WriteLine("The {0} costs {1:C} for {2} months.\n", "studio", 499.0, 3);

// Today is 06/25/2004 Console.WriteLine("Today is " + DateTime.Now.ToShortDateString());

Java

文件I/O

C#

import java.io.*;

// Character stream writing FileWriter writer = new FileWriter("c:\\myfile.txt"); writer.write("Out to file.\n"); writer.close();

// Character stream reading FileReader reader = new FileReader("c:\\myfile.txt"); BufferedReader br = new BufferedReader(reader); String line = br.readLine();  while (line != null) {   System.out.println(line);    line = br.readLine();  }  reader.close();

// Binary stream writing FileOutputStream out = new FileOutputStream("c:\\myfile.dat"); out.write("Text data".getBytes()); out.write(123); out.close();

// Binary stream reading FileInputStream in = new FileInputStream("c:\\myfile.dat"); byte buff[] = new byte[9]; in.read(buff, 0, 9);   // Read first 9 bytes into buff String s = new String(buff); int num = in.read();   // Next is 123 in.close();

using System.IO;

// Character stream writing StreamWriter writer = File.CreateText("c:\\myfile.txt");  writer.WriteLine("Out to file.");  writer.Close();

// Character stream reading StreamReader reader = File.OpenText("c:\\myfile.txt");  string line = reader.ReadLine();  while (line != null) {   Console.WriteLine(line);    line = reader.ReadLine();  }  reader.Close();

// Binary stream writing BinaryWriter out = new BinaryWriter(File.OpenWrite("c:\\myfile.dat"));  out.Write("Text data");  out.Write(123);  out.Close();

// Binary stream reading BinaryReader in = new BinaryReader(File.OpenRead("c:\\myfile.dat"));  string s = in.ReadString();  int num = in.ReadInt32();  in.Close();