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Java
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Program Structure
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C#
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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
+ "!");
}
}
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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 + "!");
}
}
}
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// Single
line
/* Multiple
line */
/** Javadoc documentation comments */
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// Single
line
/* Multiple
line */
/// XML comments on a single line
/** XML comments on multiple lines */
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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)
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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)
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// May be
initialized in a constructor
final double PI = 3.14;
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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;
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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"
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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"
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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
+
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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
+
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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++;
}
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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
}
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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);
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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);
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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;
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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;
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// Return single value
int Add(int x, int y) {
return x + y;
}
int sum = Add(2, 3);
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// Return no value
void PrintSum(int x, int y) {
System.out.println(x + y);
}
PrintSum(2, 3);
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// 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
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// Return single value
int Add(int x, int y) {
return x + y;
}
int sum = Add(2, 3);
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// Return no value
void PrintSum(int x, int y) {
Console.WriteLine(x + y);
}
PrintSum(2, 3);
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// 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
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// 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"
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// 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"
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Java
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Exception Handling
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C#
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// 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
}
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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
}
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package harding.compsci.graphics;
// Import single class
import harding.compsci.graphics.Rectangle;
// Import all classes
import harding.compsci.graphics.*;
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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;
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Java
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Classes / Interfaces
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C#
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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
{
...
}
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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 {
...
}
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Java
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Constructors /
Destructors
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C#
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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
}
}
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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.
}
}
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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.");
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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.");
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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);
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private int mSize;
public int Size {
get { return mSize; }
set {
if (value < 0)
mSize = 0;
else
mSize = value;
}
}
shoe.Size++;
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No structs in Java.
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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"
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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());
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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());
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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();
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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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