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UVA CS 101 - Review for Exam 1

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Review for Exam 1 Fall 2006 CS 101 Aaron Bloomfield Today s lecture An overview of the review sections of chapters 1 3 and 5 Stop me if you want me to something in more detail go over 2 Material you may not be comfortable with References This will come with time Using objects ifs etc It all builds over time 3 Chapter 1 4 Intro Computers think in bits 1 or 0 00101001 81 Eight bits per byte 1024 bytes 1 Kb 1024 Kb 1 Mb 1024 Mb 1 Gb 5 Computer organization CPU brain Microprocessor computer on a single chip Network when two or more computers are plugged into one another 6 Software OS the program that manages a computer s resources Program a sequence of instructions that performs some task Performing an instruction is called executing an instruction 7 Compilation Translator translates a program from one language to another Machine language the ones and zeros that a computer understands Compiler a translator which typically translates a high level language into a low level one Java is a high level language Java s compiler translates Java code into bytecode A low level language Bytecode is like machine language but not tied to a specific machine A Java bytecode interpreter is used to execute the bytecode Called a Java Virtual Machine JVM 8 Terminology Abstraction Encapsulation Similar objects exhibit similar behavior The ability to do the same thing on many objects Consider car driving example Not revealing how the method does it s work Consider String substring Consider the car radio example Modularity Dividing code into smaller pieces modules each one of which is easier to code Consider the car radio example 9 OOP stuf OOP languages A primitive type is the basic unit of storage in Java A type is a template for a variable A class is composed of types or other classes as well as methods Abstract things into the class methods Encapsulate code inside the class methods Use additional method for modularity A class is a template for an object Creating a variable object from a type class is called instantiating the type class 10 Problem solving steps Analysis Design How is it going to be done Implementation What needs to be done Make it so Testing Does it work correctly 11 Chapter 2 12 Readable programs Comments are a English text Have a before them in a Java file Blank lines make a program easier to read Indentation helps humans identify which code is within the method Keywords have special meanings in Java Examples int double class static public 13 Identifiers Identifiers programmer defined names For classes variables methods etc Cannot be a keyword Must start with a letter or or Can contain numbers also but not as the first character Good identifiers radius width position Bad identifiers x y q the really really long variable name hi mom Java default theReallyReallyLongVariableName 14 Computer bugs A bug is an error in the program To debug is to remove bugs 15 Java classes The class keyword is used to start a class declaration Can be made public for this course always do so A class is a template for an object Just as a type is a template for a variable 16 Java methods All methods have the following syntax modifers type name parameters statements Properties of the method Type that it returns public static void A name for the method main Any number The body of including zero the method of parameters can be empty String args 17 Program execution Java starts executing a program at the beginning of the main method Braces are used to specify where a method begins and ends A statement ends when a semicolon is encountered A statement can span multiple lines 18 Misc stuf A literal character string is a sequence of characters enclosed by double quotes System is the Java class that allows you to access parts of the computer system Period is used for selection Math round System in access to the keyboard System out access to the monitor Given String s select a method via s substring An exception is when Java panics It means something is wrong 19 Escape sequences Java provides escape sequences for printing special characters b backspace n newline t tab r carriage return backslash double quote single quote 20 Primitive variable types Java has 8 or so primitive types float double boolean char byte short int long real numbers two values true and false a single character integer numbers Also the void type Can make a variable final 21 Symbolic names vs literal values Which is easier to enter Math PI 3 141592653589793 Entering a symbolic name i e a constant reduces chances of errors It allows for changing the constant later on Are usually final 22 References and variables A variable is an actual spot in memory that holds a primitive type value A reference is a memory address that points to another spot in memory where the object is Variables defined in a class are initialized to a default value Variables defined in a method are not initialized to a default value 23 Math Standard operators Note that can be either integer division or floating point division computes the remainder Can provide numbers in decimal or scientific notation 24 Expressions Evaluating an expression yields a result and a type Binary operator has two operands Example 3 4 6 3 etc Left one is evaluated first Unary operator has one operand Example 4 3 yields 1 of type int Example 3 5 2 0 yields 7 0 of type double Example 3 etc Operators have precedence For example and are evaluated before and 25 Overflow Consider byte b 100 b b 100 A byte can only hold up to 127 This is called overflow Java does not tell you that this happened Underflow b b 100 26 Operators Assignment Increment and decrement Consider int i 5 System out println i System out println i int i 5 System out println i System out println i There are 4 ways to add 1 to an int i i 1 i 1 i i There are many such compound operators 27 Casting Casting converts one type to another Example int x 1 System out println double x double d 3 4 System out println int d 28 Scanner class Creating one Scanner stdin new Scanner System in Don t use Scanner create Methods public public public public public public public public int nextInt short nextShort long nextLong double nextDouble float nextFloat String next String nextLine boolean hasNext 29 Chapter 3 30 Intro An object variable is really a reference to that object null represents an object variable that points to nothing Once nothing points to an object Java automatically deletes that object Called garbage collection A final object variable Only


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UVA CS 101 - Review for Exam 1

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