Java Tutorial

Object-Oriented Programming Concepts

• Object – a representation of some item

• state fields/members and should be encapsulated• behavior methods

• Class– an implementation of some object

• Interface– the contract between classes

• Inheritance– a way to share common aspects of objects

• Package– a way to organize a set things together.

Object-Oriented Programming Concepts

super class(common aspects)

subclass(which extends the super class to specialize)

extends

Language Basics• literals (constants)• variables

– instance, class, local, parameters– data types (primitive and objects)– assignments and comparisons

• operators (unary, binary, ternary)• expressions

– comparisons • a = "hello world"; b = "hello world";• (a == b) TRUE• a.equals(b) TRUE

• i1 = new Integer(1); i2 = new Integer(1);• (i1 == i2) FALSE• i1.equals(i2) TRUE

• statements• blocks• control flow

– if/then, switch, while, do/while, for, – branching - break, continue, return

Operator Precedence

Operators Precedence

postfix expr++ expr--

unary ++expr --expr +expr -expr ~ !

multiplicative * / %

additive + -

shift << >> >>>

relational < > <= >= instanceof

equality == !=

bitwise AND &

bitwise exclusive OR ^

bitwise inclusive OR |

logical AND &&

logical OR ||

ternary ? :

assignment = += -= *= /= %= &= ^= |= <<= >>= >>>=

public class Factorial{ /* The lowest value we can compute factorial for */ public final long FACTORIAL_LOW_VALUE = 0; // constant/literal

/* The highest value we can compute factorial for */ public final long FACTORIAL_HIGH_VALUE = 20; // constant/literal /* Error message for out of range values */ public final String INVALID_FACTORIAL_VALUE = "Error: factorial can only be computed for values between " + FACTORIAL_LOW_VALUE + " to " + FACTORIAL_HIGH_VALUE + ".";

/** * …. **/ public int factorial(int x) { int factorial = 1; // local variable to this method /* * By definition factorial can only be computed * for non-negative values, hence negative * values are not allowed. */ if((x < FACTORIAL_LOW_VALUE) || (x > FACTORIAL_HIGH_VALUE)) { throw new IllegalArgumentException(INVALID_FACTORIAL_VALUE); }/* if */ for(int i = 1; i <= x; ++i) { factorial *= i; }/* for */ return factorial; }/* public int factorial(...) */}/* public class Factorial */

Classes, Parameters, and Objects

• Classes– Constructors

• when they are and not provided– Override vs Overloading Methods

• override – replaces• overloading – augments

– don’t get in the habit of using:• static initialization blocks• unnamed initialization blocks

• Parameters– passed by value

• referenced and value type parameters• Objects

– declaration– instantiation– initialization

Access Levels

Modifier Class Package Subclass World

public Y Y Y Y

protected Y Y Y N

no modifier Y Y N N

private Y N N N