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Statically Typed Language
In a statically typed language, every variable name is bound both:
- To a type (at compile time, by means of a data declaration)
- To an object
The binding to an object is optional. If a name is not bound to an object, the name is said to be null.
Once a variable name has been bound to a type (that is declared) it can be bound (via an assignment statement) only to objects of that type; it cannot be bound to an object of a different type. An attempt to bind the name of an object of the wrong type will raise a type exception.
Dynamically Typed Language
In a dynamically typed language, every variable name is (unless it is null) bound only to an object.
Names are bound to objects at execution time by means of assignment statements, and it is possible to bind a name to objects of different types during the execution of the program.
In a statically typed language, the following sequence of statements is illegal. But in a dynamically typed language this sequence of statements is perfectly file.
EmployeeName = 9
EmployeeName = "John Doe"Python and JavaScript are dynamically typed languages. Java and C++ are statically typed languages.
Weakly Typed Language
In a weakly typed language, variables can be implicitly coerced to unrelated types. Unrelated means things like numbers and strings. In a weakly typed language, the number 9 and the string “9” are interchangeable, and the following sequence of statements is legal.
a = 9
b= "9"
c = concatenate(a, b) // produces "99"
d = add(a, b) // produces 18Strongly Typed Language
In a strongly typed language, variables cannot be implicitly coerced to unrelated types, and an explicit conversion is required. (Note that I said unrelated types. Most languages will allow implicit coercion between related types – for example, the addition of an integer to a float.)
a = 9
b= "9"
c = concatenate( str(a), b)
d = add(a, int(b))Java, C++ and Python are strongly typed languages. JavaScript and Perl are weakly typed languages.