Primitives in Java Java has eight primitive types –boolean –integral types: signed: long, int, short, byte unsigned: char –floating point types: double, float Values of the primitive types are not objects –no properties –no capabilities

boolean values: true, false operations: –&&“and” –||“or” –!“not”

int values: 0, 1, -1, 2, -2, … maximum int: (= ) minimum int: (=2 32 ) operations: + - * / % 5+2 = 7+: (int,int)  int 5-2 = 3-: (int,int)  int 5*2 = 10*: (int,int)  int 5/2 = 2 (quotient) /: (int,int)  int 5%2 = 1 (remainder)%: (int,int)  int

integral types’ representations representation used differs according to whether type is signed (byte, short, int, long) or unsigned (char): –signed integral values are represented using “two’s complement” representation –unsigned integral values are represented using “binary” representation size of representation differs according to type: –byte is 1 byte wide (1 byte = 8 bits) –short is 2 bytes wide –int is 4 bytes wide –long is 8 bytes wide main point: values of different types have different representations – you can’t “mix and match”!

types of operators for type int Notice that all of these operators take two int arguments, and produce an int result. There is hardware circuitry to perform these operations.

double values: 0.0, 1.0, -3.5, e-3 inexact representation (!) operations: + - * / = 7.0+: (double,double)  double 5.0 – 2.0 = 3.0-: (double,double)  double 5.0 * 2.0 = 10.0*: (double,double)  double 5.0 / 2.0 = 2.5/: (double,double)  double

floating point types’ representation both double and float use the IEEE754 representation scheme size of representation differs according to type: –the representation of a float is 4 bytes wide –the representation of a double is 8 bytes wide main point: values of different types have different representations – you can’t “mix and match”!

mixing types in expressions Operators such as +, -, * and / are overloaded: the same name has many different values + overloaded as String concatenation too! “Good” + “ ” + “morning!”  “Good morning!” What happens in an expression which mixes values of different types? = ???? 5 is coerced to its equivalent double value, 5.0: = 7.5 Type coercion happens only from “smaller” type to “larger” type (e.g. int  double, not double  int)

relational operators We can form expressions like: x < y which have a value of true or false (i.e. the type of this expression is boolean) relational operators: >= ==

Equality testing Equality testing: –of primitive values: == –of objects: equals method Consider: Foo a = new Foo();Foo c = a; Foo b = new Foo(); what is value ofwhat is value of (a==b)(a==c)

assignment = ; evaluate, assign value to Example: int x = 5; int y = x + 3; // what value is assigned to y?

assignment Example: int x = 5; x = x + 3; // what value is assigned to x? Notice that “=” is not “equality”, but “assignment”.

Some other operators ++ increments the variable it is applied to Example int x = 5; x++;// value of x is now 6 (Caution: the value of the expression x++ is perhaps not what you would expect. The value of x++ is the value of x prior to the increment of x.)

Control structure review if ( ) true false

Control structure review if ( ) else true false

Control structure review while ( ) true false

Working with multiple objects A variable can refer to a single object: IBehavior cc = new ColorChanging(); IBehavior br = new Breathing(); A variable referring to many objects? No, but we saw how to build a composite object. IBehavior cc = new CompositeBehavior(cc,br); But it’s not too easy to add/remove items from a composite. Are there options?

Collections interface: java.util.Collection classes: –java.util.HashSet –java.util.ArrayList E is the type of element contained in the collection

Use of a collection HashSet names = new HashSet (); names.add(“Amy”);names.remove(“Bob”); names.add(“Bob”); names.add(“Cindy”); names.add(“Dave”); names.add(“Emma”); …

for-each loop for (String name : names) { System.out.println(name); } This would print out: Amy Cindy Dave Emma

Collection.shuffle Collection.shuffle(List )