Studied by 0 peopleAP Computer Science Unit 2 - Using Objects
class
defines a new data type (a classification). It is the formal implementation, or blueprint, of the attributes and behaviors of the objects of that class
object
a specific instance of a class with defined attributes.
attributes
data the object knows about itself
instance variables
variables in a class that define the attributes for objects
methods
these define the behaviors or functions for objects to describe what objects can do
constructor
creates a new object and initializes its attributes (they have the same name as the class).
new
used to create a new object; every object is created uterm-3sing the keyword new followed by a call to one of the class's constructors that initializes the object's attributes
constructor signature or header
the constructor name followed by the parameter list
method signature or header
the method name followed by the parameter list
wrapper classes
classes that create objects from primitive types, for example the Integer class and Double class
null
used to indicate that an object reference doesn't refer to any object yet
Math method: int abs(int)
Returns the absolute value of an int value (which means no negatives).
Math method: double abs(double)
Returns the absolute value of a double value.
Math method: double pow(double, double)
Returns the value of the first parameter raised to the power of the second parameter.
Math method: double sqrt(double)
Returns the positive square root of a double value.
Math.random()
Returns a random double value greater than or equal to 0.0 and less than 1.0 (not including 1.0)!
parameter list
a list of the types and variable names for the arguments being passed to a method or constructor.
overloading
creating multiple methods or constructors with the same name but different number or types of parameters.
call by value
When you call a method or constructor and give it an argument, a copy of the argument's value is saved in the parameter variable.
NullPointerException
This is the error if you try to call an object method on an object variable whose value is null
non-static or object method
These methods must be called using an object name . method name.
static method
These methods belong to a class and can be called by using the class name instead of creating an object.
return value
The value returned from a method to the calling method
strings
objects of the String class that hold sequences of characters.
index
a number associated with a position in a string (or array)
immutable
String methods do not change the String object. Any method that seems to change a string actually creates a new string.
substring
part of a string (the method will create a new string that contains a copy of part of the original string).
String method: int length()
returns the number of characters in a String object.
String substring(int from, int to)
returns the substring beginning at index from and ending at index (to - 1).
String substring(int from)
returns substring(from, length()).
int indexOf(String str)
returns the index of the first occurrence of str; returns -1 if not found.
boolean equals(String other)
returns true if this (the calling object) is equal to other; returns false otherwise.
int compareTo(String other)
returns a value < 0 if this is less than other; returns zero if this is equal to other; returns a value > 0 if this is greater than other.
substring(index, index + 1)
returns a single character at position index
autoboxing
the automatic conversion of primitive types to their corresponding object wrapper classes, for example int to Integer.
unboxing
the automatic conversion of wrapper class to the primitive type, for example Integer to int.
(int)(Math.random()*range) + min
moves the random number into a range starting from a minimum number where the range is the (max number - min number + 1)
Note
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