| 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 + "!");
}
}
} |
|
|
| // Single line
/* Multiple
line */
/** Javadoc documentation comments */ |
// Single line
/* Multiple
line */
/// XML comments on a single line
/** XML comments on multiple lines */ |
|
|
| Primitive Types
boolean
byte
char
short, int, long
float, double
Reference Types
Object (superclass of all other classes)
String
arrays, classes, interfacesConversions
// 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, enumerationsReference 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) |
|
|
| // 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; |
|
|
| enumAction {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" |
enumAction {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" |
|
|
| 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
+ |
|
|
| 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
} |
|
|
| 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); |
|
|
| 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; |
|
|
| // 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 |
|
|
| // 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.");
throwex;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.");
throwup; // 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
} |
|
|
| packageharding.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.
}
} |
|
|
| 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."); |
|
|
| 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++; |
|
|
|
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.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()); |
|
|
| 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(); |
