Java and C# Comparison

This is a quick reference guide to highlight some key syntactical differences between Java and C#. 

This is not a complete overview of either language. Hope you find this useful! 

Also see .

Java

Program Structure

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

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<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

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 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

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: 02/01/2011 06:45:24 

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