Detailed introduction to code comparison between JAVA and C#

JavaProgram StructureC#
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 + "!"); } } }
JavaCommentsC#
// Single line /* Multiple line */ /** Javadoc documentation comments */	// Single line /* Multiple line */ /// XML comments on a single line /** XML comments on multiple lines */
JavaData TypesC#
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)
JavaConstantsC#
// 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;
JavaEnumerationsC#
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"
JavaOperatorsC#
Comparison == < > <= >= != Arithmetic + - * / % (mod) / (integer pision 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 pision if both operands are ints) Math.Pow(x, y) Assignment = += -= *= /= %= &= |= ^= <<= >>= ++ -- Bitwise & | ^ ~ << >> Logical && || & | ^ ! Note: && and || perform short-circuit logical evaluations String Concatenation +
JavaChoicesC#
greeting = age < 20 ? "What&#39;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&#39;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 }
JavaLoopsC#
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);
JavaArraysC#
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;
JavaFunctionsC#
// 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&#39;t need initializing TestFunc(a, ref b, out c, p1, refp2); 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
JavaStringsC#
// 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"
JavaException HandlingC#
// 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 }
JavaNamespacesC#
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;
JavaClasses / InterfacesC#
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 { ... }
JavaConstructors / DestructorsC#
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&#39;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. } }
JavaObjectsC#
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&#39;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&#39;s type: " + obj.GetType().ToString()); if (obj is SuperHero) Console.WriteLine("Is a SuperHero object.");
JavaPropertiesC#
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++;
JavaStructsC#
聽 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"
JavaConsole I/OC#
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&#39;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());
JavaFile I/OC#
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();

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