Java MidTerm Chp 1 to 5 and 7

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index/subscript

the number corresponding to each position in the array.

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array size

size N is indexed from 0 to N-1.

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height[8]

refers to the single variable stored at that memory location.

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array

is an object. To create an array the reference variable for the array has to be declared and then instantiated using the new operator. An array can be set up to hold primitive types or object (class) types. all same type or compatible.

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int[] height = new int[size];

variable height is declared to be an array of integers whose type is written as int[]. The new operator reserves the memory space to store size.

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array element

A value stored in an array.

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element type

Type of data that can be stored as an element in a particular array.

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int[] list = new int[LIMIT]; for (int value : list) System.out.print(value + " ");

this iterator version of the for loop is used to print all the values in the array.

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bounds checking

ensures that an index used to refer to an array element is in range. if index is not valid and ArrayIndexOutOfBoundsException is thrown. Automatic in Java.

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off-by-one errors

created by processing all but one element or by attempting to index one element too many.

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arrayName.length

attribute of array object and holds the size of the array. This is the size and the index is length - 1.

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initializer list - int[] scores = {87,98,69,87};

A list of values delimited by braces and separated by commas, used to initialize the values stored in an array. The new operator does not need to be used to instantiate the array object.

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array passed to a method

An array is an object and the entire array can be passed as a parameter. A reference to the array is passed to the method. Any changes made to the array element will be reflected outside the method. The formal parameter is an alias to the original.

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an element of an array passed to a method

if the element type is a primitive type, a copy of the value is passed. if the element type is a reference to an object, a copy of the object reference is passed.

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String[] words = new String[5];

array words holds references to String objects. The new operator instantiates the array object and reserves space for five string references. The objects that are stored in each element must be instantiated separately.

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mean1 = average(42,69,37,10); public double average(int ... list) for(int num:list) list.length

parameter list in a method header allows a variable number of parameters to be passed in, which are stored in an array for processing. int is the type of array element, ... indicates a variable number of parameters, list is the name of the array.

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one dimensional arrays

represents a simple list of values

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two-dimensional array int[][] table = new int[5][10];

represents a simple list of values. thought of as rows and columns of a table. Array of arrays or one-dimensional array of references to one-dimensional integer arrays.

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multi-dimensional array

array with more than one dimension.

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class

a class is a blue-print of an object. The class represents the concept of an object. It defines the variables and methods that are part of every object instantiated from it.

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objects

objects have states defined by values of the attributes and behaviors defined by the operations/methods associated with that object. Objects are generally nouns the methods of the class are the verbs.

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members of a class

members are the data and methods of a class collectively. objects can invoke member methods.

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toString method

is a method of any object gets called automatically whenever you pass the object to a print or println method. the default toString defined for every object is generally not useful.

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scope

scope of the variable is the area within a program in which the variable can be referenced.

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instance variable

declared at the class level, can be referenced in any method of the class. Each instance of the class has its own version of the variable.

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modifier

private, protected, public.

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public method

service method for an object because it defines a service that the object provides.

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private method

support method it cannot be invoked from outside the object and is used to support the activities of other methods in the class

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intialization of any variables declared at class level

Java automatically initializes any variables declared at the class level.

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UML

Unified Modeling Language class diagrams to show the contents of classes and the relationships among them.

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encapsulation

guarding data from inappropriate access. Make it difficult or impossible for code outside a class to "reach in" and change values of a variable that is declared inside the class.

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client

code that uses an object

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final - private final static int NUMBER = 10

constant. final modifier are often declared using the static modifier.only need one copy of the value across all objects of the class.

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accessor methods

a method that provides read-only access to a particular value. getters.

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mutator methods

a method that changes a particular value. setters.

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method declaration

specifies the code that is executed when the method is invoked. called method is the invoked method. the calling method invoked it.

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driver programs

drive the use of other more interesting parts of a program often for testing purposes.

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return statement

method that returns a value. when a return statement is executed the control is immediately returned to the statement in the calling method. and processing continues there. Not good practice to have more than one return statement.

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Constructors

no return type. it initializes the variables associated with each object. default constructor that take no parameters are automatically provided if no constructor is provided.

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parameters

provide data to a method that allow the method to do its job. when method is called the parameter is copied and stored in corresponding formal parameter. literals, variables, or full expressions.

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parameter list

provides the type of value that is passed into the method, and the name by which the called method will refer to each value.

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formal parameter

name of the parameters in the header of the method declaration

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actual parameters or arguments

values passed into a method declaration and invocation is enclosed in parentheses after the method name.

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local data

variable declared in a method is local to that method and cannot be used outside of it.

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static variable and methods private static int count = 0;

static variable aka class variable are shared among all instances of a class. Only one copy for all objects of the class. Memory space for static variables are established when the class that contains it is referenced for the first time in the program

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static methods - public static int getCount()

static methods aka class method can be invoked through the class name. Do not need to instantiate an object of the class in order to invoke the method. static and main methods can access only static and local variables.

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has - a relationship

aggregation-is composed, at least in part, of other objects. A class that is defined in part by another class is dependent on that class.

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is - a relationship

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uses - relationship

one class relies on the functionality of the other. Dependency relationship.

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this reference

this reference can be used to refer to the currently executing object.this reference refers to the object through which the method was involked. Often used in constructors but sometimes in other methods.

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algorithm

step by step process for solving a problem. ie recipe.

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pseudocode

mixture of code statements and English phrases.

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pass by value

All parameters are passed by value. The current value of the actual parameter is copied into the formal parameter in the method header. separate copy of the value that is passed in, any changes made to it have no effect on the actual parameter.

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method overloading

same method name with different parameter lists for multiple methods.

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signature

Method's name along with the number, type and order of its parameters. Compiler uses the complete method signature to bind a method invocation to appropriate definition. Return type is not part of the signature.

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regression testing

running previously administered tests again to make sure all issues are resolved.

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defect testing

testing to find errors.

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black box testing

test cases are developed without regard to the internal workings. they are based on input and outputs

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white box testing or glass box testing

test case is based on logic of the code. Goal is to make sure that every path through the program is executed. aka statement coverage.

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unit testing

creates a test case for each module of code(method) that has been authored.

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integration testing

all modules that were individually tested during unit testing are now tested as a collection

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system testing

seeks to test the entire software system and how its implementation adheres to its reuirements.

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test driven development

test cases are developed for code before the code is written.

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debugging

correcting run-time and logic errors.

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flow and control

is the order in which statements are executed in a running program. program flow is usually linear. Invoking a method alters the flow of control.

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conditional statement/ selection statement

allows us to choose which statement will be executed next. if - else statements and switch, each decision is based on a boolean expression also called condition that evaluates to true or false.

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loop or repetition statement

allows a program to execute a statement multiple times. s loop is based on a boolean that determines how many times the statement is executed.

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equality operators

==, !=

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relational operators

>, <, <=, >=

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logical operator

!, &&, ||. && and || short circuit.

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block statement

several statements can be grouped together into a block statement enclosed in braces. { }

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conditional operator

is a ternary operator requires three operands. (condition) ? true : false;

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comparing floats

floats equal only if the binary digits of the underlying representaions match. should rarely use == when comparing floating point values. Use Math.abs() of the difference between two numbers.

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comparing objects

Can not use equality or relational operators to compare object. for strings can use equal or equalsIgnoreCase(), compareTo().

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switch

switch (idChar){ case 'A': action break; default: action; } can only be of type char, byte, short, or int

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sentinel

indicates the end of the input.

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control C

interrupts an infinite loop

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break statement

is used to stops execution of a loop. break statements are avoided in a loop.

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continue statement

loop condition is evaluated again the loop body is executed again if it is still true. continue statements are voided in a loop

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iterator

is an object that has methods that allows you to process a collection of items one at a time. hasNext(), next

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hasNext

iterator object that returns a boolean value indicating whether there is at least one more item to process.

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iterator object that returns the next input token as a string.

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import java.io.*;

text file input Scanner fileScan, urlScan: fileScan = new Scanner(newFile("websites.inp"));

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creating objects - String name;

creates a String variable that has a reference to a String object. An object variable does not hold the object itself, it holds the address of an object.

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creating objects

someobject != null someobject = null; //make sure it is a valid object prior to using it.

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new operator

creates an object. it instantiates an object which returns the address of the new object. After the new operator creates the object, a constructor is invoked to help set it up initially.

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dot operator

is used to access the instantiated objects methods.

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garbage collection

The process of reclaiming memory space that can no longer be used by a program.

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immutable

An object whose data (state) cannot be modified once it is created.

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String objects

cannot be lengthened or shortened nor can any of its characters change. string has methods: char charAt(int index) part of the string class java.lang package

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char charAt(int index) string class java.lang package

returns char at specified index.

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int compareTo(String str) string class java.lang package

Returns neg number if this string is lexically before the string str,0 if equal, or positive number if after the string str. stringObjName.compareTo("compareString");

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String concat(String str) string class java.lang package

returns new concat string

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boolean equals(String str) string class java.lang package

true if contains same characters as str, false otherwise

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boolean equalsIngnoreCase(String str) string class java.lang package

true if same otherwise false.

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int length() string class java.lang package

returns the number of characters in this string

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String replace(char oldChar, char newChar) string class java.lang package

returns new string identical with this string except every occurrence of oldChar is replaced by newChar.

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String substring(int offset, int endIndex) endIndex is total number including what you are offsetting, offset start cnt at 1

returns new string that is a subset of this string starting at index offset and extending through endIndex-1. Change is inevitable, except from vending machines. mute.substring(3,30) nge is inevitable, except f

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String toLowerCase() String toUpperCase() string class

returns lower or upper case.

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class library

a collection of classes that we can use when developing program.

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JAVA API

application programming interfaces standard class library that is part of any java development environment. ie System, Scanner, String.... are part of Java API

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package

language-level org mechanism for classes. Each class in Java API belongs to a particular package. ie String class is part of java.lang package, System class java.lang package, Scanner java.util

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fully qualify reference

import java.util.Scanner; - asserts Scanner class of java.util package may be used in the program.

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import with asterisk(*) or wildcard

indicates any class inside the package might be used in the program.good only if 2 or more class are used from same package. import java.util.*;

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java.lang

All classes of java.lang package are automatically imported for every program.

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java.math

math package. performs calculations with high precision

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java.text

format text for output

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java.util

General utilities.

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Random class - java.util package

random number generator picks a number out of a range of values.

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Random() java.util.Random;

Constructor: creates a new pseudo number generator

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float nextFloat() java.util.Random;

returns a random number between 0.0 and 1.0

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int nextInt() java.util.Random;

random number that ranges over all possible int values(pos or neg)

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int nextInt(int num) java.util.Random;

random number in the rang 0 to num-1. import java.util.Random; Random generator = new Random(); num = generator.nextInt(20) + 10; produces an int in 0-19 range and shift results by 10 to 10-29

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Math class

part of the java.lang package and contains all static methods aka class methods. only need class name to invoke. Math.abs(total);

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static int abs(int num)

returns absolute value of num. static math class method in java.lang

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static double pow(double num, double power)

returns the value num raised to the power. static math class method in java.lang

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static double random()

returns random number between 0.0 to 1.0. static math class method in java.lang

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static double sqrt(double num)

returns square root of num, which must be a pos. static math class method in java.lang

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NumberFormat class

java.text. package

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DecimalFormat class

java.text package

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factory methods java.text. package

static NumberFormat getCurrencyInstance and static NumberFormat getPercentInstance because they produce and return an instance of an object set up in a particular manner. NumberFormat fmt1 = NumberFormat.getCurrencyInstance(); fmt1.format(totalcost);

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String format(double number) both java.text.NumberFormat and java.text.DecimalFormat

returns a string with specific number formatting. DecimalFormat fmt - new DecimalFormat("0.###"); fmt.format(doublevariableName);

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enumerated type

enum Season {winter, spring, summer, fall}; Season time; time = Season.spring; time.ordinal(); time.name(); time // will return name

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ordinal value

enumerated type is stored as an integer which starts at 0. time.ordinal();

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wrapper classes

represent a particular primitive type. ie byte Byte, int Integer, boolean Boolean, char Character. Wrapper class contains static methods. - num = Integer.parseInt(str); - Integer class contains MIN_VALUE & MAX_VALUE.

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Integer(int value) / wrapper method

num = Integer.parseInt(str);

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autoboxing

auto conversion of a primitive type to a corresponding wrapper object. Integer obj1 int num1 = 69; obj1 = num1 // auto creates int object to reverse Integer obj2 = new Integer(69); int num2; num2 = obj2; // auto extracts int value

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\b,\n, \t, \r, \", \\, \'

escape sequences, is a series of characters that represents a special character.

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variable

is a name for a location in memory used to hold a value of a particular data type.

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assignment operator =

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strongly typed

Java is strongly typed not allowed to assign a value to another data type.

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primitive data types

integers, floating points, char, boolean data types. floating points are float or a double. Integers are byte, short, int, or long. All numeric types are signed (-,+).

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float ratio = 0.2363F

literal

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long countedStars = 86827263927L

literal

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precedence

+, - RtoL *, /, % LtoR +, -, +concat LtoR = R to L

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postfix prefix

count++; //count = count +1; total = count++; total = 15 and count = 16; ++count; total = ++count; total = 16 and count = 16;

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+= -= *= /=

assignment operator. total = total +5;

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conversion techniques

float sum; int count; result = sum/count; result will be a float casting: (int) (double)

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String next() java.util.Scanner

returns next input token as a character string

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String nextLine() java.util.Scanner.

returns input remaining on the current line as a character string.

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double nextDouble() float nextFloat() int nextInt() java.util.Scanner

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boolean hasNext() scan.hasNext() java.util.Scanner

returns true if the scanner has another token in its input.

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// /* */ /** javadoc*/

Comments are ignored by the computer and do not affect how the program executes.javdoc generates external documentation from the comments.

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Java is case sensitive

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white space

blanks, tabs, and newline characters used to separate words and symbols in a program. extra white space is ignored.

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Java bytecode

low-level representation of Java source code program. Java compiler translates source code into bytecode which can be executed using Java interpreter. bytecode is transportable across Web. java is architecture neutral.

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Syntax rules

define how symbols and words of a programming language can be put together.

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4 basic activities in software development

requirement analysis, design, implementation, and testing.

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primary element that support object-oriented programming

objects, classes, encapsulation, and inheritance.

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errors

compile-time error - no executable created run-time error - crash or term abnorm logical error - program compiles and executes but produces incorrect data

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inheritance

reuse. one class can be used to derive serveral new classes.

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application

program

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software

consist of programs and the data those programs use

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program development

writing, translating, investigating.

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basic programming steps

edit & save program, translated program executable, execute program.

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IDE

integrated development environment combines tools into one software program.

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development environment

set of tools used to create, test, and modify programs. NetBeans

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aliases

two or more references that refer to the same object are aliases of each other.

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