Differencebetween an Int and an Integer in Java and C#

What is the difference between an int and an Integer in Java and C#?

In Java, the 'int' type is a primitive, whereas the 'Integer' type is an object.

In C#, the 'int' type is the same as System.Int32 and is a value type (ie more like the java 'int'). An integer (just like any other value types) can be boxed ("wrapped") into an object.

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The differences between objects and primitives are somewhat beyond the scope of this question, but to summarize:

Objects provide facilities for polymorphism, are passed by reference (or more accurately have references passed by value), and are allocated from the heap. Conversely, primitives are immutable types that are passed by value and are often allocated from the stack.

Difference between int and Integer

part 1

One example .. you can use Integer as the key of HashMap but you can't use int. Because an Object is needed.

So where you need an int value as an object there you need to use Integer class.

part 2

++i is pre increment
i++ is post increment

for example

i = 0;
System.out.println(i++) //will print 0 then the i will be 1.

and

i = 0;
System.out.println(++i) // here i wil be incremented first then print 1.

Difference between int and new int()

int myNumber;

int myNumber = 0;

int myNumber = new int(); 

The effect should be exactly the same, you can try to ILDASM them if you're doubtful

Is there any difference between String and string in C# like int and Integer in Java?

No. string is an alias for String.

Same as:

int ==> Int32
double ==> Double

and others.

Difference between char (int) and int

As it can be seen, the integer splits. For quite a while, I am unable to figure it out?

You are not reading integers, you are reading bytes which have characters encoded as ?ASCII?

Is there a way where I can save the console value into an integer, as I would be using this value in the future?

The simplest way is to use a Scanner

Scanner scanner = new Scanner(in);
while (scanner.hasNextInt()) {
   // read bytes up the next whitespace, parse as a int
   int n = scanner.nextInt();

Difference Between int[] and list int

On the wire they will be indistinguishable - i.e. both Customer[] and List<Customer> are going to look (roughly) like:

<Customers>
   <Customer name="Fred" ... />
   <Customer name="Barney" ... />
</Customers>

So there is no point having logic that treats the two differently. Ultimately, int[] is a pain to work with (Add etc), so I would tend to use List<T> - of course, wsdl.exe nicely defaults to arrays, IIRC - but there is a command line switch (or perhaps there is for wse/wcf).

What is the difference between int, Int16, Int32 and Int64?

Each type of integer has a different range of storage capacity

   Type      Capacity

   Int16 -- (-32,768 to +32,767)

   Int32 -- (-2,147,483,648 to +2,147,483,647)

   Int64 -- (-9,223,372,036,854,775,808 to +9,223,372,036,854,775,807)

As stated by James Sutherland in his answer:

int and Int32 are indeed synonymous; int will be a little more
familiar looking, Int32 makes the 32-bitness more explicit to those
reading your code. I would be inclined to use int where I just need
'an integer', Int32 where the size is important (cryptographic code,
structures) so future maintainers will know it's safe to enlarge an
int if appropriate, but should take care changing Int32 variables
in the same way.

The resulting code will be identical: the difference is purely one of
readability or code appearance.

Difference between C# and Java's ternary operator (? :)

Looking through the C# 5 Language Specification section 7.14: Conditional Operator we can see the following:

• If x has type X and y has type Y then

  • If an implicit conversion (§6.1) exists from X to Y, but not from Y to X, then Y is the type of the
    conditional expression.

  • If an implicit conversion (§6.1) exists from Y to X, but not from X to Y, then X is the type of the
    conditional expression.

  • Otherwise, no expression type can be determined, and a compile-time error occurs

In other words: it tries to find whether or not x and y can be converted to eachother and if not, a compilation error occurs. In our case int and string have no explicit or implicit conversion so it won't compile.

Contrast this with the Java 7 Language Specification section 15.25: Conditional Operator:

• If the second and third operands have the same type (which may be the null type), then that is the type of the conditional expression. (NO)
• If one of the second and third operands is of primitive type T, and the type of the other is the result of applying boxing conversion (§5.1.7) to T, then the type of the conditional expression is T. (NO)
• If one of the second and third operands is of the null type and the type of the other is a reference type, then the type of the conditional expression is that reference type. (NO)
• Otherwise, if the second and third operands have types that are convertible (§5.1.8) to numeric types, then there are several cases: (NO)
• Otherwise, the second and third operands are of types S1 and S2 respectively. Let T1 be the type that results from applying boxing conversion to S1, and let T2 be the type that results from applying boxing conversion to S2.
  
  The type of the conditional expression is the result of applying capture conversion (§5.1.10) to lub(T1, T2) (§15.12.2.7). (YES)

And, looking at section 15.12.2.7. Inferring Type Arguments Based on Actual Arguments we can see it tries to find a common ancestor that will serve as the type used for the call which lands it with Object. Object is an acceptable argument so the call will work.

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