Java vs C# – Part 1

Disclaimer: long post!

Introduction

While some of my friends and colleagues seem to think that I don’t like Java and that I am some sort of Microsoft/.NET zealot, that is actually not true! Smile with tongue out I do like Java, and I worked with it for several years.

There are several articles out there on the differences and similarities between C# and Java, but none actually satisfied me. In this new series of posts, I will try to explain these similarities and differences, as extensively and accurately as I can. I don’t want to start a religious war, but I won’t refrain from emitting judgments on what I think is best in each. I will try to cover as much as I can, but I won’t drill into APIs, instead will focus on each language’s intrinsic characteristics.

This first post will focus on high-level constructs, what I call structure: namespaces and types. I will be covering Java 8 and C# 5, the latest (as of February 2015) versions of these languages.

Update: See the second post here.

Similarities

Both languages (Java and C#) are case-sensitive, strictly object oriented, offering classes, enumerations and interfaces, single inheritance model and all of the types live in namespaces/packages. Also, all support attributes/annotations, methods and fields, including static ones. The base class for all types, in both cases, is called Object. Both have the same basic operators, comparable base types and exception handling mechanisms. Both start executing by a static method called main/Main.

Compiled Units

A Java class compiles to an identically-named class file; these files exist on their own, but are usually stored together inside a jar, war or ear, which are basically ZIP files with a manifest file attached to, for better manageability. These files, of course, can contain other resources, such as images or text files.

C# classes always exist in binary assemblies, which can have two basic forms (extensions):

  • dll: a library, does not run on its own;
  • exe: a stand-alone executable, which can either be a Console or a Windows Forms / Windows Presentation Foundation graphical application.

Assemblies can also include metadata and embedded resources, of any type. C#/.NET actually defines another compilation unit, the module, but typically a module matches an assembly, although it is possible to have it other way, for more advanced scenarios.

Namespaces

Both in Java and in C# we have the notion of namespaces or packages, which can be nested. In C#, the namespace declaration must wrap all of its types, and therefore we can have several namespace declarations in a source file, even nested:

namespace MyNamespace1
{
    public class Class1
    {
    }
}
 
namespace MyNamespace2
{
    public class Class2
    {
    }
 
    namespace MyNamespace3
    {
        public class Class3
        {
        }
    }
}

In Java, the package declaration goes on the top of a source file, meaning, it can only contain a single package:

package myPackage;
 
public class MyClass
{
}

There is one important difference between Java and C#: in Java, the namespace must be identical to the physical folder structure, that is, a class belonging to the a.b package must be physically located in an a\b folder; Java won’t compile it otherwise. The generated .class file must be located in the same folder, such as a\b\MyClass.class.

Java and C# can simplify accessing classes in other namespaces/packages by importing these, like we see here for Java, where we can import all types (*), or a type at a time:

//import java.lang.*;    automatically imported
import java.io.*;
import java.lang.reflect.Array;

Java imports automatically the types in the java.lang package, C# does not automatically import any namespace, and it doesn’t allow importing a single type:

using System;
using System.IO;

But it also lets us define type aliases per source file using the same syntax:

using date = System.DateTime;
 
public class MyClass
{
    public date GetCurrentDate()
    {
        //...
    }
}

Top Level Elements (Types)

Java and C# offer a very close syntax, in some cases, if we discount the different language conventions, it’s really hard to tell one from the other, but there are some important differences.

Java offers the following top level elements, besides packages:

  • Classes (including generic);
  • Interfaces (including generic);
  • Enumerations.

And C# the same plus some more:

  • Classes (including generic);
  • Interfaces (including generic);
  • Enumerations;
  • Structures;
  • Delegates (including generic).

Basic Types

The basic types in the two languages (C#/Java) are:

  • Object/Object (C# shorthand: object);
  • String/String (C# shorthand: string);
  • Byte/byte (C# shorthand: byte);
  • SByte/N/A (C# shorthand: sbyte);
  • Boolean/boolean (C# shorthand: bool);
  • Char/char (C# shorthand: char);
  • Int16/short (C# shorthand: short);
  • UInt16/N/A (C# shorthand: uint);
  • Int32/int (C# shorthand: int);
  • UInt32/N/A (C# shorthand: uint);
  • Int64/long (C# shorthand: long);
  • UInt64/N/A (C# shorthand: ulong);
  • Single/float (C# shorthand: float);
  • Double/double (C# shorthand: double);
  • Decimal/N/A (C# shorthand: decimal);
  • dynamic/N/A;
  • Arrays.

As you can see, C# offers unsigned and signed versions of all integer types and also a high-precision Decimal type. It also as a dynamic type, used for late-binding (runtime) operations without strong compile-time checks.

C# offers three kinds of arrays:

  • Single dimension: int [] numbers;
  • Multi dimension: int [,] matrix;
  • Arrays of arrays, also called, jagged arrays: int [][] matrix;

Java also has single dimension and jagged arrays, but no multi dimension ones.

C# lets us use the var keyword for declaring a variable and automatically initializing it. This is a shorthand for the initialization’s type:

var i = 10;            //int
var s = "string";      //string
var f = SomeMethod();  //method's return type, except void

In C# as in Java, we can specify suffixes for clarifying the desired type of a literal:

  • 10n: integer;
  • 10l: long;
  • 10f: float;
  • 10d: double;
  • 10u: unsigned int (C# only);
  • 10ul: unsigned long (C# only);
  • 10m: decimal (C# only).

Both lowercase or uppercase letters are allowed as the suffix.

Classes

Classes in Java and C# are allocated in the heap. A class can inherit from a single base class, if not specified, it will inherit from Object. It can implement any number of interfaces.

Structures

C# has a unified type system, meaning, primitive types (integers, floating points, booleans, etc) coexist in the same type hierarchy as composite classes. This is different in Java, where, for example, the int and Integer types are not related, even if it is possible to convert between the two. All primitive types in C# are structures, not classes, which means they are allocated in the stack instead of the heap. In Java this also occurs for primitive types, but there is no notion of explicit structures, and we can’t build our own types to be stored in the stack. A structure in C# cannot inherit from any class explicitly, but it can implement any number of interfaces, and also cannot declare a destructor/finalizer:

public struct MyStructure : IMyInterface
{
    public void MyMethod()
    {
    }
}

Structures and enumerations in C# are called value types and classes and interfaces are called reference types. Because of C#’s unified type system, a structure always implicitly inherits from System.ValueType.

Interfaces

In C#, an interface can only have:

  • Instance method declarations;
  • Instance property declarations;
  • Instance event declarations.

It can be generic or non-generic. Both classes and structures can implement interfaces. An interface can always be assigned null, it is a reference type. Also, a generic interface in C# can be made covariant or contravariant.

In Java, things are a bit different, since they can have also have statics and (the horror!), method implementations:

  • Instance method declarations;
  • Fields (always implicitly static) with a value (constants);
  • Default methods: methods with default implementations.

They can also be generic or otherwise, and can be implemented by enumerations. In Java, an interface's members can also have visibility levels defined, that is, they are not always public.

If a Java interface only has one method, or, at least, one non-default method (more on this later), it can be marked as a functional interface, in which case, it can be used in lambda functions, the method is implicitly called (see an example below in the Delegates section).

Generic Types

Generics are quite different, internally, in Java and C#. Both languages support generic classes and interfaces, but in C# they are a first-class construct, with reflection support, but in Java they cease to exist once a generic class is compiled. That is, in Java, a List<String>, at runtime, becomes just List, the generic parameter String is erased, this is in order to ensure backward compatibility with prior Java versions that didn’t have generics. This doesn’t happen in C#, and we can at runtime reflect on a generic class and its parameters.

Both languages support any number of generic parameters and constraints on them. In C# these constraints are:

  • Base class, structure or interface: forces the generic parameter to inherit or implement from a specific class, structure or interface;
  • Public non-abstract class with a public parameterless constructor: only allows generic parameters that are non-abstract (or interfaces) and have a public constructor that doesn’t take parameters;
  • Reference or value type: a generic parameter either has to be a reference (class or interface) or a value type (structure or enumeration), as specified.

An example:

public class GenericClassWithReferenceParameter<T> where T : class
{
}
 
public class GenericClassWithValueParameter<T> where T : struct
{
}
 
public class GenericClassWithMyClassParameter<T> where T : MyClass
{
}
 
public class GenericClassWithPublicParameterlessParameter<T> where T : new()
{
}
 
public class GenericClassWithRelatedParameters<K, V> where K : V
{
}
 
public class GenericClassWithManyConstraints<T> where T : IDisposable where T : new() where T : class
{
}

Java accepts the following constraints:

  • Base class: a generic parameter must inherit from a base class;
  • Implementing interface: a generic parameter must implement some interface;
  • Unbounded generic type: a generic parameter must inherit/implement some generic type.

Some examples:

public class GenericClassWithBaseClassParameter<T extends BaseClass>
{
}
 
public class GenericClassWithInterfaceParameter<T extends Interface>
{
}
 
public class GenericClassWithBaseMatchingParameter<T, ? super T>
{
}
 
public class GenericClassWithManyInterfaceParameters<T implements BaseInterface1 & BaseInterface2>
{
}
 

In Java, we can specify a generic of an unknown type:

MyInterface<?> var;

Java also has some terrible limitations:

  • There cannot be generics of primitive types, for example, MyGenericClass<int>, only of non-primitives, like MyGenericClass<Integer>;
  • There cannot be generic arrays.

Because C# supports any kinds of generic parameters, if we want to initialize explicitly some variable of a generic parameter type, we need to use the default keyword:

public class MyGenericClass<T>
{
    public void MyMethod()
    {
        T someField = default(T);
    }
}

Finally, the base class of some class inheriting from a generic type is not that generic type, but its base class, which can seem awkward. This happens in C# and in Java.

Delegates

A delegate in C# is a method signature, composed of:

  • A name;
  • A return type;
  • Parameters (number and type).

Delegates are the building blocks of events. A delegate can either point to a static, an instance or an anonymous method (lambda), provided the signature is the same:

public delegate double Operation(double v1, double v2);
 
//a delegate pointing to a static method
Operation addition = Operations.Add;
 
//a delegate pointing to an instance method
Operation subtraction = this.Subtract
 
//a delegate pointing to an anonymous method using lambdas
Operation subtraction = (a, b) =>
{
    return a + b;
};

A delegate can be generic:

public delegate void Action<T>(T item);

Delegates inherit automatically from System.Delegate, because of this, they have built-in support for dynamic and asynchronous invocation.

Java has a similar construct, functional interfaces. These are interfaces with a single non-default method, which can be used in lambda functions:

public interface MyWorkerFunction
{
    @FunctionalInterface
    public void doSomeWork();
}
 
public void startThread(MyWorkerFunction fun)
{
    fun.doSomeWork();
}
 
public void someMethod()
{
    startThread(() -> System.out.println("Running..."));
}

If an interface is marked as functional but has more than one method, it will not compile.

Enumerations

Enumerations in Java can have members (constructors, fields and methods) and even implement interfaces, something that is not possible in C#:

public enum MyEnumeration implements MyInterface
{
    A_VALUE(1),
    ANOTHER_VALUE(2);
 
    private int value;
 
    private MyEnumeration(int value)
    {
        this.value = value;
    }
 
    public static String fromInt(int value)
    {
        if (value == A_VALUE.value) return ("A_VALUE");
        else return ("ANOTHER_VALUE");
    }
}

In C#, no methods or interfaces, but we can have an enumeration be implemented based on a primitive integer type, including unsigned (the default is signed int):

public enum MyEnumeration : uint
{
    AValue = 1,
    AnotherValue = 2
}

Implicitly, all C# enumerations inherit from System.Enum.

In both cases, C# and Java, we can specify integral values for each enumeration member, and, if we don’t, members will get sequential values.

Type Visibilities

A type in Java has four possible visibilities:

  • package: only accessible by other classes in the same package (the default);
  • public: accessible by everyone.

And C# types have similar ones, plus one:

  • internal: only accessible by other classes in the same assembly (the default);
  • public: accessible by everyone.

Inheritance

In C#, the syntax for extending a class and for implementing an interface is exactly the same:

public class MyClass : BaseClass, IInterface
{
}

Whereas in Java there are the extends and the implements keywords, respectively, for classes and interfaces:

public class MyClass extends BaseClass implements Interface
{
}
 
public interface DerivedInterface extends BaseInterface1, BaseInterface2
{
}

Both can inherit from a single class and implement as many interfaces as desired. Also, an interface can itself inherit from several interfaces.

In C# it is possible to implement interfaces in one of two ways:

  • implicit: where the interface’s members are directly accessed through the implementing class;
  • explicit: where we have to cast the class to the explicitly implemented interface before we can use it; this is useful, among other reasons, if we want to implement several interfaces which offer identically-named members.

Let’s see how they look in C#, in this example, interface IMyInterface1 is explicitly and IMyInterface2 implicitly implemented:

public class MyClass : IMyInterface1, IMyInterface2
{
    void IMyInterface1.MyMethod1()
    {
    }
 
    public void MyMethod2()
    {
    }
}

Explicitly-implemented members are always private and cannot be virtual or abstract. If we want to call a method or access a property of an explicitly implemented interface, we need to cast the instance first:

MyClass c = new MyClass();
IMyInterface1 i = (IMyInterface1) c;
i.MyMethod();

Java only has implicit interface implementations:

public class MyClass implements MyInterface
{
    public void myMethod()
    {
    }
}

Inner Classes

In Java as in C#, we can have multiple levels of nested/inner classes, structures and interfaces, but in Java they can be static or instance:

public class MyClass
{
    public static class MyStaticInnerClass
    {
    }
 
    public class MyInnerClass
    {
    }
}

Instance inner classes can only be instantiated when we have an instance of its containing class (do notice the awful syntax):

MyClass.MyStaticInnerClass c1 = new MyClass.MyStaticInnerClass();
 
MyClass c2 = new MyClass();
 
MyClass.MyInnerClass c3 = c2.new MyInnerClass();

In C#, any inner class can be instantiated, with or without an instance of the containing class, provided its visibility level is respected:

public class MyClass
{
    public class MyInnerClass
    {
    }
}
 
MyClass.MyInnerClass c = new MyClass.MyInnerClass();

For C# the following visibility levels exist:

  • internal: only accessible by other classes in the same assembly (the default);
  • protected: only accessible by descending classes;
  • protected internal: derived classes or classes from the same assembly;
  • private: only accessible by the declaring class;
  • public: accessible by everyone.

Whereas for Java:

  • package: only accessible by other classes in the same package (the default);
  • protected: only accessible by descending classes;
  • private: only accessible by the declaring class;
  • public: accessible by everyone.

Abstract Classes

In Java as in C# we have abstract classes, and the syntax is exactly the same:

public abstract class MyClass
{
    public abstract void myMethod();
}

C# structures cannot be abstract.

Sealed Classes

Both frameworks allow a class to be marked as sealed/final, meaning, it cannot be inherited from:

public sealed class MyClass
{
    //a C# sealed class
}
public final class MyClass
{
    //a Java final class
}

C# structures are always implicitly sealed.

Static Classes

In C# we can have static classes, which are roughly equivalent to being at the same time abstract and sealed. Static classes only allow static members (properties, methods, fields and events):

public static class MyClass
{
    public static void MyMethod()
    {
    }
 
    public static string MyField;
 
    public static int MyProperty { get; set; }
 
    public static event EventHandler MyEvent;
}

Java does not have the concept of static classes.

Nullable Types

Because it is allocated in the stack, a variable of a structure or enumeration type always has a value, so, it cannot be null, but we can use a handy syntax to turn it into a nullable type, which can itself be made null:

int ? nullableInteger = null;
nullableInteger = 1;
 
if (nullableInteger.HasValue)    //if (nullableInteger != null)
{
    int integer = nullableInteger.Value;    //int integer = nullableInteger
}

In Java, primitive values can never be null, we need to resort to their corresponding wrapper classes:

Integer nullableInteger = null;
nullableInteger = new Integer(1);

Classes and interfaces in C# (reference types) are always nullable, meaning, can always be assigned null.

Partial Classes

C# allows marking a class as partial, meaning, its contents may spread through several different source files; the actual compile-time class will be built from all of these files. This is very useful when we have automatically generated files that we don’t want to change, but rather complement:

//in file MyClass.Generated.cs
public partial class MyClass
{
    public void OneMethod()
    {
    }
}
 
//in file MyClass.cs
public partial class MyClass
{
    public void AnotherMethod()
    {
    }
}

Anonymous Classes

Java has anonymous classes: we can create anonymous classes that implement some interface or extend some class, by implementing all of its abstract methods:

this.addEventListener(new ListenerInterface
{
    public void onEvent(Object source, Event arg)
    {
    }
});

Anonymous classes in C# do not contain explicitly defined methods, only read-only properties; two anonymous classes are considered of the same type if their members are declared in the same order and with the same types:

var i1 = new { A = 10, B = "" };
var i2 = new { A = 1000, B = "string" };
 
//these two classes have the same type
i1 = i2;

In order to support anonymous classes, C# introduced the var keyword, which allows us to have a variable infer its type automatically. An anonymous type is created when a variable is created without a static type.

Type Members

In .NET we have the following type members:

  • Constructors (static and instance);
  • Destructors;
  • Methods (static and instance);
  • Fields (static and instance);
  • Properties (static and instance);
  • Events (static and instance);
  • Overridden operators and type conversions (discussed on the next post).

Java only has:

  • Constructors (static and instance);
  • Constructor blocks;
  • Destructors;
  • Methods (static and instance);
  • Fields (static and instance).

Static Constructors

Static constructors or class initializers are basically the same in C# and Java, but have a slightly different syntax, here is the Java one:

public class MyClass
{
    static
    {
        //do something the first time the class is used
    }
}

And the C# syntax:

public class MyClass
{
    static MyClass()
    {
        //do something the first time the class is used
    }
}

Java offers another weird thing: constructor blocks. You can have any number of them, and their code will be included automatically into all of the class’ constructors:

public class MyClass
{
    {
        System.out.println("First constructor block, called before constructor");
    }
 
    public MyClass()
    {
        System.out.println("MyClass()");
    }
 
    {
        System.out.println("Second constructor block, called before constructor but after first constructor block");
    }    
}

Destructors

In C# a destructor, or finalizer, is just a shorthand syntax to the Finalize method. This method is called by the Garbage Collector when an instance is about to be freed. Java has an identical method, called finalize, which serves a similar purpose. Strictly speaking, none of these methods is actually a destructor, but they are sometimes called that.

In C#, we can use the C++ syntax instead of overriding Finalize:

public class MyClass
{
    ~MyClass()
    {
        //object is being freed
    }
}

Static Members

Unlike C#, Java allows referencing static members through an instance variable, for example:

public class MyClass
{
    public static void doSomething()
    {
    }
}
 
MyClass c = new MyClass();
c.doSomething();

Properties

Properties are a useful C# construct, which allows a cleaner syntax to changing fields:

public class MyClass
{
    public int MyProperty { get; set; }
}
 
MyClass c = new MyClass();
c.MyProperty++;

We can have auto-implemented properties (such as in this example) or properties with an explicit backing field:

public class MyClass
{
    private int myField;
 
    public int MyProperty
    {
        get
        {
            return this.myField;
        }
        set
        {
            this.myField = value;
        }
    }
}

The Java equivalent can only be achieved with methods:

public class MyClass
{
    private int myProperty;
 
    public void setMyProperty(int value) { this.myProperty = value; }
    public int getMyProperty() { return this.myProperty; }
}
 
MyClass c = new MyClass();
c.setMyProperty(c.getMyProperty() + 1);

In C# we can also define indexed properties for classes, interfaces and structures, like in this example using an integer index:

public class MyCollection
{
    private Object [] list = new Object[100];
 
    public Object this[int index]
    {
        get
        {
            return this.list[index];
        }
        set
        {
            this.list[index] = value;
        }
    }
}

We are not limited to integer indexes, any type can be used as the key to an indexed property.

Finally, properties can have different visibility levels for the getter and setter methods, and can even have just one of them (usually just a setter does not make much sense):

public int InternalProperty
{
    get;
    private set;
}
 
public string GetOnlyProperty
{
    get
    {
        return this.InternalProperty.ToString();
    }
}

Events

Events are C#’s implementation of the Publisher/Subscriber and Observer Patterns: it allows to register methods that will be called when the event is raised, and offers a simple syntax for registering, unregistering and clearing event handlers. An event handler is just an instance of a delegate, the delegate is the event’s signature:

public class MyClass
{
    public event EventHandler MyEvent;
 
    public void ClearEventHandlers()
    {
        //check for registered event handlers
        if (this.MyEvent != null)
        {
            //raise event
            this.MyEvent(this, EventArgs.Empty);
 
            //clear event handlers
            this.MyEvent = null;
        }
    }
}
 
MyClass a = new MyClass();
 
//register event handler
c.MyEvent += OnMyEvent;
 
//unregister event handler
c.MyEvent -= OnMyEvent;

Like with properties, it is also possible in C# to implement the event add and remove methods explicitly, so as to add our own behavior:

public class MyClass
{
    private EventHandler myEvent;
 
    public event EventHandler MyEvent
    {
        add
        {
            this.myEvent += value;
        }
        remove
        {
            this.myEvent -= value;
        }
    }
}

Automatic Initialization of Fields and Properties

All fields declared in a class are initialized to their type’s default value (0 for integers and floating point number, false for booleans, null for classes). C#’s auto-implemented properties are also implicitly initialized to their type’s default value. This behavior is the same in both languages, of course, Java does not have properties.

Member Visibilities

C# has four visibility levels for members:

  • private: accessible from the declaring type;
  • internal: accessible from types in the same assembly as the declaring type;
  • protected: accessible from types inheriting from the declaring type;
  • protected internal: accessible from types either inheriting from the declaring type or from its same assembly;
  • public: accessible by everyone.

And Java, we only have:

  • package: only accessible by classes in the same package;
  • protected: only accessible by descending classes;
  • private: only accessible by the declaring class;
  • public: accessible by everyone.

Virtual Members

In Java, all methods are virtual by default (there is no virtual keyword), unless marked as final.

In C#, a method, property or event needs to be explicitly marked as virtual so that it can be overridden, and all overrides must state so:

public class MyBaseClass
{
    public virtual void MyMethod()
    {
    }
}
 
public class MyDerivedClass : MyBaseClass
{
    public override void MyMethod()
    {
    }
}

If a derived class member with the same name as one in the base class exists, but it is not an override of it, we need to mark it as new:

public class MyBaseClass
{
    public void MyMethod()
    {
    }
}
 
public class MyDerivedClass : MyBaseClass
{
    public new void MyMethod()
    {
        //no relation with MyBaseClass.MyMethod
    }
}

Sealed Members

In C# as in Java, it is possible to mark a member (method) as sealed/final, meaning, it is not available for overriding in a derived class. In C# the same applies to events and properties, which, of course, don’t exist in Java.

C# syntax:

public class MyClass
{
    public sealed void DoSomething()
    {
    }
}

And Java syntax:

public class MyClass
{
    public final void doSomething()
    {
    }
}

Abstract Members

In both languages, abstract members (methods) can exist in abstract classes, but they are not required: we can have abstract classes without any abstract members. In C#, besides methods, we can also have abstract properties and events.

Generic Methods

Methods can also be generic, regardless of living in generic classes or not. The same constraints apply, but generic methods also have automatic type inference:

public class MyClass
{
    public static int Compare<T>(T v1, T v2)
    {
        if (v1 == v2)
        {
            return 0;
        }
 
        return -1;
    }
}
 
//no need to specify the int parameter type
int areEqual = MyClass.Compare(1, 2);

Read-only and Constant Fields

Both Java and C# have read-only fields, but C# uses the readonly keyword:

public static class Singleton
{
    //a C# readonly field
    public static readonly Singleton Instance = new Singleton();
}

And Java uses final:

public class Singleton
{
    //a Java final field
    public static final Singleton INSTANCE = new Singleton();
}

C# also offers another kind of read-only field, constants. A constant is always static and can only be of one of the primitive types, or an enumerated value:

public static class Maths
{
    //a C# constant field
    public const double PI = 3.1415;
}

The difference between readonly and const is that the C# compiler inlines all constants, that is, it actually replaces any references to it by their concrete values. The Java compiler does something similar for static final fields. Read-only fields can be initialized inline, together with the field declaration, or in constructors (static or instance).

Technical Review

I couldn’t have written this post without the technical review by my friend and colleague Roberto Cortez (@radcortez), of Java fame. Thanks, Roberto! Winking smile

Next Steps

That’s it for now. Stay tuned for the next post, where I will talk about other language differences. Let me hear from you!

                             

15 Comments

  • Ummmm. The latest version of C# is C#6 (current in preview). C#5 has been live for quite a while now....

  • Hi, Isaac!
    Yeah, my mistake! Updated, thanks!

  • > For both C# and Java, the same visibility levels exist for nested classes as for global ones.

    Actually in C# a nested class can be private, protected or protected internal, unlike a global class.

    > C# properties can also be indexed

    You can only create an indexer for a class, not for a property.

  • Dirk:
    1) So, you are saying that a nested class cannot be public...? The visibilities are what I said: public, private, protected, protected internal and internal, see https://msdn.microsoft.com/en-us/library/ms173120.aspx;
    2) True, bad choice of words.

  • I'm saying that in addition to being public or internal like a normal class, a nested class can also be private, protected and protected internal.

  • Dirk:
    Clarified, thanks!

  • You say, "Both Java and C# have read-only fields, but C# uses the readonly keyword".

    C#'s readonly isn't the same as in Java. In C#, if a field is marked readonly, it can be modified in a constructor. So it's not the same as a "static final" field in Java.

    I like the article, though!

  • Greg:
    Thanks, but a field in Java can be final without being static and can be initialized in the constructor. Not sure I understood you correctly, what do you mean?

  • >Delegates ...
    >Java has no analogous construct.

    Java does have the analogue: functional interfaces, which are more powerful.

  • Hi, Alex!
    True; even though I mentioned functional interfaces, it is worth mentioning them here also. Updated, thanks!

  • BTW, don't actually think they are more powerful... .NET delegates have built-in support for dynamic invocation, asynchronous invocation, they are covariant, etc

  • > If an interface is marked as functional but has more than one method, it will not compile.

    This is also not true. Functional interface can have multiple methods, but additional methods need to be implemented by the interface itself and marked as default.


    @FunctionalInterface
    public interface Iterable<T> {
    Iterator<T> iterator();

    default void forEach(Consumer<? super T> action) {
    Objects.requireNonNull(action);
    for (T t : this) {
    action.accept(t);
    }
    }
    }

  • C#'s anonymous classes also override Equals and GetHashCode. Which makes them very handy as Dictionary keys.

  • Robert Giesecke: yep, thanks!

  • Byte/byte (C# shorthand: byte); SByte/N/A (C# shorthand: sbyte); =>

    Byte/N/A (C# shorthand: byte); SByte/byte (C# shorthand: sbyte);

    java's byte is signed

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