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CSIII – Unit 2 Exam
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VOCABULARY LIST
Term
Definition
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class
Blueprint to make object
object
Instance of a class
reference
Variable storing the address of an object
constructor
Special method invoked to create an object
initialize
To give an initial value to a variable
immutable
Not changeable
index
Numerical position of a character in a String object
instantiate
To create an object
new
Java operator used to make an object
null
A reserved word indicating a reference refers to no object.
package
a. Group of classes in the Java API
import
keyword used to specify a class(es) used in a program
method
Things an object can do
static
reserved word indicating a method can be invoked using Class name instead of an object
KEY CONCEPTS
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CREATING OBJECTS
o You create (“instantiate”) objects using the new operator
o The variable used to refer to your object is known as a “reference variable”/remote control
o You can have more than one variable referring to the same object (aliases)
STRINGS
o The characters in a string object are numbered starting at zero (index)
o String objects have several methods you can use on them
 substring(int start, int end) - start is inclusive, end is not (return part of the string)
 length() – return length of string
 replace (char oldChar,newChar) – replace one char with another char
PACKAGES
o All classes in the Java bible (API) are contained in a package
o The java.lang package is automatically imported into your program
o You must import classes you wish to use in your program (except ones from java.lang)
RANDOM CLASS
o Code to create a random generator: Random generator = new Random( )
o nextInt(num) – returns an integer from 0 (inclusive) to the num specified (exclusive)
o nextFloat( ) – returns a decimal value from 0 to 1.0 (exclusive)
MATH CLASS
o Has several static methods you can use (invoke as Math.____)
o Examples: Math.pow(2,5) = 32 Math.sqrt(16) = 4
FORMATTING OUTPUT
o 2 classes can be used (NumberFormat, DecimalFormat)
o DecimalFormat you specify format using # 0 $ , % (0 – means show zero in your answer)
WRAPPER CLASSES
o Use these to create objects for the primitive data types. There is one wrapper for each primitive type
o Wrappers: Integer, Double, Float, Character, Boolean, Long, Short