Beginning of Year Review

AP Computer Science A

Objectives

• Define variables and explain how they are used in computer programming
• Explain what a "strongly typed" language means
• Identify errs related to variables
• List primitives used in Java

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Variables

• Variables are used to manage a computer's memory locations
• Each variable relates to a memory location
• Each variable controls the contents of that memory location
• Assignment operator ' = ' is used to store a value in that memory location
• Amount of memory needed is depended upon type of value

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Variables

• Specify type of values to be stored - strongly typed language
• Type of value can Not be changed for a particular variable
• ie. loss of precision err int sum = 3.5;

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• Err - "Cannot not find symbol"
• not been declared
• Err - "might not have been initialized"

int sum;

Declaration statement

sum = 3.5;

Assignment Statement

Variables

• Naming conventions:
• letters, numbers, _, $ allowable
• Can not begin with a number
• No spacing (special character)
• Class name begins with capital letter

Primitive Data Types

char

• 16 bits
• unicode
• 'a', 'T', '('
• default: \u0000

Null

boolean

• 1 bit
• true or false
• default: false

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byte

• 8 bits

short

• 16 bits

int

• 32 bits

long

• 64 bits

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• default: 0 for each

float

• 32 bits
• 0.0f

double

• 64 bit
• 0.0d

Check for understanding

Activity:

AP Classroom 1.2 Variables

Numbering Systems

Numbering Systems

Base 10 - decimal

• 0-9

Base 16 - hexadecimal

• 0-9, a-f

Base 2 number - binary

• 0, 1

Base 8 number - octal

• 0-7

Doubles and Scientific Notation

• Decimal numbers that have more than seven digits to the left of the decimal point are printed in scientific notation.
• 123456789.123 = 1.23456789123E8

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• Java considers any number named in scientific notation to be a floating point number
• 4E3 = 4000.0

Casting

• The process of changing a value of one data type into a value of another data type
• int a = (int) 2.5; narrowing
• without the cast an error will be returned - loss of precision
• Java will implicitly store an int as a double
• double a = 5; returns 5.0 widening
• double a = (double) 5;

Arithmetic Expressions

• Arithmetic operators: *, /, %, +, -, (order of precedence)
• - (subtraction) is unary operator: only one operand needed
• -a
• Operands can be variables or literals
• sum = a + 2;
• average = sum / 3.5

Arithmetic Expressions

• Five shorthand arithmetic operators:
• += ? same as a=a+ ?
• -= ? same as a=a- ?
• *= ? same as a=a* ?
• /= ? same as a=a/ ?
• %=? same as a=a% ?

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? = a number literal or variable

Arithmetic Expressions

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• Either operand is a double, then the other operand will (if necessary) be implicitly cast to a double and the result will be a double.
• a = 5 + 3.2 ... a=5.0+3.2 ... results in a double 8.2
• c = 5 + (int) 3.2 or c = (int) (5+3.2)

Arithmetic Expressions

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• Calculations are not always exact
• All integers lie in the range from Integer.MIN_VALUE through Integer.MAX_VALUE
• Calculation whose result lies outside this range - overflow - strange things can happen.

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Check for Understanding

AP Classroom

1.3 Expressions

Strings

• String phrase = "Hello World";
• String literal
• Each letter is a character
• Location is index - begins at 0
• Number of character is length ( .length() )
• Escape Sequence indicate with \ (backslash)
• \" , \n, \\

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String Concatenation

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• Build a String with two or more shorter Strings
• "Go " + "Jaguars" evaluates to Go Jaguars
• + operator concatenates if both operands are Strings
• + operator adds if both operands are double or int
• + operator concatenates if first operand is String

String Methods

• int length() // number of characters in String

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• String substring(int from, int to)

// returns the substring beginning at from and ending at to-1

• String substring(int from)

// returns substring(from, length())

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String Methods

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• int indexOf(String str)

// returns the index of the first occurrence of str; returns -1 if not found

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• int compareTo(String other)

// returns a value < 0 if this is less than other

// returns a value = 0 if this is equal to other

// returns a value > 0 if this is greater than other

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String to Number Conversion

• Integer.parseInt
• String to int

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• Double.parseDouble
• String to a double

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• Double.toString
• double to String
• " " + 5.2;

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• Integer.toString
• int to String
• "" + 6;

IMACS Ex. 29

Check for Understanding

AP Classroom 2.7_StringMethods

Booleans

• Java provides six relational operators:

<, <=, >, >=, ==, and !=

• compare values
• relational expression or boolean expression

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Resources

Data Types: Florida Institute of Technology - http://cs.fit.edu/~ryan/java/language/java-data.html

Data Types: Oracle Java Documentation - https://docs.oracle.com/javase/tutorial/java/nutsandbolts/datatypes.html

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