Computer Science 1026 Topic 2.docx

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Computer Science
Computer Science 1026A/B
Brian Langen

Topic 2: Introduction to Java and Dr Java Dr Java?  Dr Java is an integrated development environment (IDE) for Java programming o Writing the code, compiling, running, debugging can be done in this one program  Dr Java has several panes o Definition pane: Used for creating (tying in and editing) complete java programs o Interaction pane: Used for testing of specific code without having to compile; unique to Dr Java o Files pane: All currently open and used classes are listed here. Arithmetic Expressions  To try out Dr Java, we will begin with simple math: evaluating arithmetic expressions  Arithmetic expressions consists of operands (values) and operators and represent a numeric value o Addition: + o Subtraction: - o Multiplication: * o Division: / o Negation: – o Modulo: % (Remainder after integer division. Returns whole numbers without any decimal points)  Default evaluation order: o Parentheses () o Negation – o Multiplication, division, and modulo from left to right o Addition, and subtraction, from left to right o Add parentheses even in unnecessary situations to make it clear what is happening o Think like the computer! The computer cannot reason or think and jump ahead. Notion of Type  Java is a strongly-typed language  Every value has a „type‟ associated with it, which tells how the computer to interpret values. Primitive Data Type  Used to store simple data values, such as integers, floating points, characters, and Booleans.  Used for efficiency reasons, as they take very little memory, and allow fast computation.  Each type stores a specific range of numbers within a specific amount of memory.  Integer Values: o Stores whole numbers only. „Int‟ is used most often. o Byte: Uses 8 bits. Holds range of numbers between -100 to 100. o Short: Uses 16 bits. Holds range of numbers between -32,000 to 32,000. o Int: Uses 32 bits. Holds range of numbers between -2.1 billion to 2.1 billion. o Long: Uses 64 bits.  Floating Point Values: o Stores all real values in scientific notation. „Double‟ is used most often. o Float: Uses 32 bits. o Double: Uses 64 bits.  Casting: o Changes the type of one of the integer type value to a floating point value type (or vice versa) o More often used when there are variables holding values, instead of actual numbers.  Ex. Casting 3 in (3 / 2) to a double: (double) 3 / 2 o Not always necessary. Adding a .0 at the end of a number can have the same effect.  Characters o Stores a single value of any alphabets, numbers, or symbols using Unicode encoding. o Char: Uses 16 bits  Booleans o Compares two operands of the same type with relational operators. o Holds only „true‟ or „false‟. o Relational Operators:  Greater than: >  Less than: <  Equal: ==  Not equal: !=  Greater than or equal: >=  Less than or equal: <= String  String: Object variable-type for any length of a sequence of characters o Strings represent all text data o Objects are not limited in size, so strings can have as many characters as wished. o Java compiler recognizes strings as beginning and ending with a double quotation  Null string: A string with no values, and is represented by double quotes with nothing in between “”  Concatenation: Java can add (or concatenate) multiple strings using the concatenation operator: + o The result of this is a new string with the characters of second strings written after characters of the first  Ex. System.out.println(“CS1026” + “a” + “/” + “b”) = CS1026a/b o Numbers can also be concatenated with strings changing the numbers into strings, then concatenating them  Ex. System.out.println(“The total is” + 10) = The total is 10  Escape Character: Special character (\) that is used to allow special characters to be embedded into a string o Add a double quotation : \” o Add a \: \\ o Add a tab: \t o Move to the next line: \n Java Statements  Java programs are made up of unique statements for programming  Java statements end in a semicolon. Having missing semicolons lead to syntax errors.  Ex. Assignment Statement: o Assignment statements are used to assign a variable a new value o =; to assign the value of a variable to what comes after the =  Ex. Print-out Statement: o Print statements are used when a value needs to be outputted. o System.out.println(); to print the value of the expression between the parenthesis, then move to a new line o System.out.print(); to print the value of the expression between the parenthesis without moving to a new line Variables  Variables: Locations in memory containing a value, and labeled with a name o Called „variable‟ because the content can vary, depending on what the programmer stores or calculates o Variables can be created and named by declaring, an
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