Primitive Types • Java supports two kinds of types of values • objects, and • values of primitive data types • variables store • either references to objects (address in memory) • or directly primitive values (bit patterns) • bit patterns is interpreted according to the primitive type • primitive types • int, byte, short, long • integer numbers only different precision (32, 8, 16, 64 bits) • double, float • floating point numbers only different precision (64, 32 bits) • char • characters (letters, digits, special characters) • boolean • logical values true or false
Operators • primitive types support operators • typically binary, but also unary and even ternary • used in expressions • arithmetic operators • numeric operands, result is the more precise number type • byte, short, int, long, float, double • +, -, *, /, % (modulo) • +, -(sign change, unary) • relational operators • primitive types operands, boolean result • == (=),!= (≠); (works also with objects!) • <,>,<= (≤),>= (≥) • logicaloperators • boolean operands, booleanresult • & (and), | (or)), ^ (xor) • && (and), || (or) • short circuit, i.e. second operand is evaluated only if necessary • ! (not, unary)
Other Operators • + (String concatenation) • instanceof (tests whether an object has certain type) • <<,>>,>>>,~,&,|,^ • (bit pattern operations with numeric operands) • there are overloaded operators • e.g., +: unary sign, binary addition, String concatenation • operand type or usage decide meaning • ternary operator <op1> ? <op2> : <op3> • <op1> must be boolean • result is <op2> if <op1> is true • result is <op3> if <op1> is false • e.g., int minimum = i < j ? i : j;
Assignment Operators • increment and decrement operators • x++; means x = x + 1; • x--; means x = x - 1; • there is also ++x and --x; don't use it! • most operators can be combined with an assignment • meaning: x <op>= y; means x = x <op> y • x += y; means x = x + y; • x -= y; means x = x - y; • x *= y; means x = x * y; • x /= y; means x = x / y; • x %= y; means x = x % y; • don't ever use assignment operators within an expression • Java allows is, but it's only source of errors • x++ + y; if different from ++x + y • x += y -= z; what the heck does it?
Operator Precedence • precedence = the order in which operators are evaluated: • () • +, -, !(unary) • *, /, % • +, - • <,>,<=,>= • ==,!= • & • | • ^ • && • || • on the same level, operators are evaluated left to right
Numeric Types • integer types • byte (8 bits) • short (16 bits) • int (32 bits) • long (64 bits) • result of division by zero is an error • overflow is not an error! • byte,short stored in one 32-bit word • long stored in two 32-bit words • long constants have L suffix, e.g., long m = 1000L; • hex constants start with0x prefix, e.g., byte hex = 0x2f3a; • floating point types • float (32 bits; 24 bits mantissa, 8 bits exponent) • double (48 bits mantissa, 16 bits exponent) • special value NaN (undefined) • result of division by zero is NaN • overflow is an error • float constants have F suffix, e.g., float x = 1000F; • Additional support in package java.lang • classes Byte,Short, Integer, Long, Float, Double
Type char • represents characters • constants are enclosed in single quotes, e.g., char digit = '9'; • constants can be defined numerically with C suffix, e.g., char ch = 0C; • is ordered, but the order is crazy • first some special characters • then lowercase 'a'..'z' • then more special characters • then uppercase 'A'..'Z' • then other special characters.. • then digits '0'..'9' • then other characters • Unicode standard • 16 bits, but stored in one 32-bit word • supports most at languages • Chinese, Kanji, Hiragana, Katakana, Korean, Thai, Arabic, … • compatible with integer types • e.g., int lowercase = 'q'; • char uppercase = (char) (lowercase + 'A' - 'a'); • Additional support in class Characterin package java.lang
Type boolean • two values true and false • operand ! (not) • ! true is true • ! false is false • operands &, && (and) • are both operands true? • true & true is true • true & false is false • false& true is false • false & false is false • also: only true & true is true • also: both operands must be true so that result is true • also: if one of the operands is false the result is false • &: evaluate both operands then compare • &&: evaluate first operand, if it's false then don't evaluate second • only if it's true evaluate second operand and compare
Type boolean • operands |, || (or) • is at least one operand true? • true | true is true • true | false is true • false| true is true • false | false is false • also: only false | false is false • also: both operands must be false so that result is false • also: if one of the operands is true the result is true • |: evaluate both operands then compare • ||: evaluate first operand, if it's true then don't evaluate second • only if it's false evaluate second operand and compare • operands ^ (xor) • are both operands different? • true ^ true is false • true ^ false is true • false^ true is true • false ^ false is false • also: both operands must have the same value so that result is false • also: operands must have different values so that result is true
Use of boolean • computation with logical values • variables of type boolean • e.g. boolean done = false; • to return result from a method • asking existence, e.g., hasOutline() • asking for truth of a property isVisible() • conditional decisions • if a condition is true do something • otherwise do something else • repeat doing something while a condition is true • special branching and looping statements • if statement • if-else statement • switch statement • while statement • for statement
