Java与C#语法对比及转换

转载自：https://blog.csdn.net/eray/article/details/1553731 

 

Java (J2SE 5.0) and C# Comparison
This is a quick reference guide to highlight some key syntactical differences between Java and C#.
This is by no means a complete overview of either language. Hope you find this useful!
Also see VB.NET and C# Comparison.

 

Comments Data Types Constants Enumerations Operators

Choices Loops Arrays Functions Strings

Exception Handling Namespaces Classes / Interfaces Constructors / Destructors Objects

Properties Structs Console I/O File I/O

 

Java Comments C#
// Single line /* Multiple     line  */ /** Javadoc documentation comments */	// Single line /* Multiple     line  */ /// XML comments on a single line /** XML comments on multiple lines */
Java Data Types 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 Constants 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 Enumerations 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 Operators 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 Choices 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 Loops 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	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 Arrays 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 Functions 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 Strings 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 Exception Handling 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 Namespaces C#
package harding.compsci.graphics; import harding.compsci.graphics.Rectangle;  // Import single class import harding.compsci.graphics.*;   // Import all classes	namespace Harding.Compsci.Graphics {   ... } or namespace Harding {   namespace Compsci {     namespace Graphics {       ...     }   } } // Import all class. Can't import single class. using Harding.Compsci.Graphics;
Java Classes / Interfaces 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 Constructors / Destructors 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 Properties 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 Structs 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 Console 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 File 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();

Page last modified: 02/03/2006 07:15:58

Copyright © 2004 by Frank McCown
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