Java Data Types#
I am studying the Java programming language in AP CS A. Here are a few quirks I noticed about data types in the language.
Primitives vs. objects#
Java is an object-oriented programming language. It forces you to write classes. There are no
such things as standalone functions or variables. Ironically, not everything is an “object” in Java.
int i = 0;
short s = (short)42;
byte b = (byte)25;
long l = 2412346987L;
double d = 3.1415926;
float f = 3.14f;
boolean b = true;
char c = 'a';
The code above gives examples of values that are not objects. These values are called “primitives”, which means that sadly, there are no methods available for these objects. While one may argue that methods are seldom used on integers, booleans, and floating point numbers, sometimes they do come in handy. Here is an example in Python to check for an alphabetic character:
"A".isalpha()
As opposed to the equivalent code in Java:
Character.isLetter('A');
The Java version is just more typing. In fact, in order to use methods on those primitives, Java
created “wrapper” classes for each of the primitives, which is very confusing to me. In addition
to Character, there are Double, Integer, etc.
Converting data types#
Notice how I created a short above in Java with the following statement:
short s = (short)42;
The reason why I did this is that Java only allows implicit type conversion from smaller data types
to larger data types. 42 is an int (32 bits) while short only holds 16 bits, so we must cast
explicitly.
Note
There is no such issue with Java objects. Variable holding objects are actually holding references to them, which are all of the same size.
Conclusion#
This is all I have for today. Next time I’m going to talk more about Strings in Java.