Primitive Types CSE 115 Spring 2006 April 3 &

Type  A set of values and the operations we can do with those values.

Object Types vs. Primitive Types  We have been using object types all semester.  Primitive types are another type built into Java.  The distinction between these two types has been significantly blurred by Java 5.

Primitive Types  Primitive Types ≠ Objects  The way we create them is different.  Primitive types have a value.  Objects have instance variables.  Primitive types have operations we can perform on them.  Objects have methods we can call on them.

Types of Primitives  Numbers  Booleans  Characters

Numbers  Whole Numbers  byte – 1 byte (-128 to 127)  short – 2 bytes  int – 4 bytes ( to )  long – 8 bytes

Operations on Numbers (Unary) +  Promotes a byte, short or char to an int -  Unary negation ++  Increment --  Decrement

Operations on Numbers (Binary) +  Addition -  Subtraction *  Multiplication /  Division %  Modulus

Important Note  In Java, operations on integers are closed. This means that an operation performed on an integer returns an integer, or likewise, an operation performed on two integers returns an integer.

More Numbers  Real/floating point numbers  float  double  Operations: Same as for whole numbers

Important note  Operations on two real numbers return a real number.  Operations on a real number and a whole number return a real number.

How to get the “real” answer to the division of two integers?  Typecasting – we can force Java to believe that we are doing floating point arithmetic. int a = 1; int b = 2; double realAnswer = (double)1/2;

Booleans  Two-valued algebra system  True  False  The boolean values in Java are true and false (not 0 and 1).

Operations that return boolean values <  Less than >  Greater than <=  Less than or equal to >=  Greater than or equal to ==  Equals !=  Not equals

Operations performed on booleans (Unary)  Negation (not)  Symbol: !  Meaning: p!p truefalse falsetrue

Operations performed on booleans (Binary)  Conjunction (and)  Symbol: &&  Meaning:  Disjunction (or)  Symbol: ||  Meaning: pq p && q truetruetrue truefalsefalse falsetruefalse falsefalsefalsepq p || q truetruetrue truefalsetrue falsetruetrue falsefalsefalse

Short circuit boolean evaluation  Java supports short circuit boolean evaluation.  This means that if there is a false in a conjunction or a true in a disjunction, Java stops evaluating the expression and produces the result.

Characters  Single letter, digit, or symbol  Character literals are surrounded by ‘’ in code: char aCharacter = ‘x’;  Character class has methods of interest when working with characters.

String  Not a primitive type  Sequence of characters  String literals are surrounded by “” in code String greeting = “Hi there!”;

String concatenation  Can combine strings together using the + operator. String one = “light”; String two = “house; String result = one + two;  result now has the value “lighthouse”

String concatenation  You can also combine a string with a primitive type. int a = 5; int b = 6; int result = a * b; String output = “The result of multiplying 5 and 6 is: ” + result;

String Class  There are many useful methods for String available in the String class.