Differences in comparision with Java

• Return type is mandatory for recursive functions. This is because, for non-recursive functions, Scala evaluates the right hand side of the function to find out the return type. This is not always possible in case of recursive functions that do not terminate.

• There are no premitive types in Scala. Everything is a class.

• When a variable is declared and initialized, it's type is inferred. However it is advisible to specify the type if the variable is being initialized to 'null'.

var x = null        // x will be of type Null
x = 2               // this will result in error as 2 is of type Int

var y: Int = null    // now the type of y will be Int and not inferred as Null
y = 2                // Success

• Scala string is same as java.lang.String. However Scala string has over 100 methods that are not available in Java. So refer to Scaladocs before coming up with a complex operation on Strings. Look for StringOps in Scala docs.

  "Hello".intersect("World")    // gives 'lo'
  

• The ++, -- operators do not exist in Scala. Use += instead: counter += 1;

• An Int is automatically converted to a RichInt when one of it's method is needed. e.g.: 1.to(10) automatically converts 1 to a RichInt type and applys 'to( )' method on it.

• Infix notation:

For methods with only one parameter, you could write as below
1.to(10) OR 1 to 10. This is called infix notation.
Conversly, 1 + 2 can also be expressed as 1.+(2) althought it's a bit weird.

• Scala has both functions and methods. Methods operate on Objects where as functions don't operate on Objects, they are more like static methods. However there are static methods in Scala, the ones that are inherited from Java classes. But usually they are not written.

• When invoking a method on an object, you use paranthesis in front of the method if the method is a mutator, not otherwise.

  e.g: "Hello".distinct        // gives Helo
  

• Method call apply need not be specified.

  e.g: "Hello".apply(4) and "Hello"(4) are both same and yield 'o'
  

• Unlike in java or any other language, if is an expression with a value. The result of if can be assigned to a variable. Since if has a value, it needs to have a type. In case the if and else are of different type, the type of expression will be super type. Any can be thought of equivalent of Object in java.

if(x > 0) "positive" else -1        // type of if is 'Any'

• Blocks are also expressions in Scala. The result of block is the result of last expression within the block.

• There is no three part for loop in scala

  for(int i = 0; i < n; i++)    // compile error
  instead do
  for(i <- 1 to n)
  

• Scala supports named parameters like Python. You can name the parameters when calling the function. Advantage is that the parameters can be out of order and Scala takes care of arranging them at run time.

• Scala also supports Default Arguments.