c# 与 java 语法异同

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 + "!");
    }
}

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 + "!");
      }
   }
}

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)

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)

// Can be set to a const or a variable. May be initialized in a constructor. 
readonly int MAX_HEIGHT = 9;

// 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 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"

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
+

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
+

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++;
}

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
}

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);

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);

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;

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;

// 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

// 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 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 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"

try {
  y = 0; 
  x = 10 / y;
} catch (Exception ex) {
  System.out.println(ex.getMessage()); 
} finally {
  // Code that always gets executed
}

try {
  y = 0; 
  x = 10 / y;
} catch (Exception ex) {      // Variable "ex" is optional
  Console.WriteLine(ex.Message); 
} finally {
  // Code that always gets executed
}

// Import single class
import harding.compsci.graphics.Rectangle;

// Import all classes
import 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;

// Inheritance
class FootballGame extends Competition {
  ...
}

// Interface definition
interface IAlarmClock {
  ...
}

// Extending an interface 
interface IAlarmClock extends IClock {
  ...
}

// Interface implementation
class WristWatch implements IAlarmClock, ITimer {
   ...
}

// Inheritance
class FootballGame : Competition {
  ...
}

// Interface definition
interface IAlarmClock {
  ...
}

// Extending an interface 
interface IAlarmClock : IClock {
  ...
}

// Interface implementation
class WristWatch : IAlarmClock, ITimer {
   ...
}

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   
  }
}

public SuperHero() {
     mPowerLevel = 0;
  }

public SuperHero(int powerLevel) {
    this.mPowerLevel= powerLevel; 
  }

~SuperHero() {
    // Destructor code to free unmanaged resources.
    // Implicitly creates a Finalize method.
  }
}

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.");

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.");

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);

public int Size { 
  get { return mSize; } 
  set { 
    if (value < 0) 
      mSize = 0; 
    else 
      mSize = value; 
  } 
}

shoe.Size++;

No structs in Java.

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"

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());

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());

// 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();

// 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();