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67 Cards in this Set
- Front
- Back
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instance methods |
requires that an instance of a class be created in order to be used
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static fields/methods |
the class name rather than the instance name is used |
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static fields |
declared using the static keyword between the access specifier and the field type |
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static methods |
declared by placing the static keyword between the access modifier and the return type of the method necessary to create an instance of the class in order to use the method may be called at the class level typically used to create utility classes such as the MATH class may not communicate with instance fields |
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passing objects as arguments |
passes value of the reference variable |
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reference variable value |
an address or reference to the object in memory a copy to the object is not passed, just a pointer to the object possible for the method to modify the contents of the object referenced by the variable |
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returning objects from methods |
methods can return references to objects as well as primitive data types a copy of the argument is not returned, only its address
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toString method |
can be called explicitly called implicitly when you pass an object of the class to println or print and when you concatanate an object of the class with a string all objects have this method that returns the class name and a hash of the memory address of the object the default method can be overridden with your own to print more useful info
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equals method |
when the == operator is used with reference variables, the memory address of the object are compared, the contents of the objects are not compared all objects have this method the default operation of this method is to compare memory addresses of the objects just like == |
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methods that copy objects |
reference only copy deep copy |
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reference only copy |
copying the address of an object into another reference variable
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deep copy |
involves creating a new instance of the class and copying the values from one object into the new object |
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copy constructors |
accepts an existing object of the same class and clones it |
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aggregation |
creating an instance of one class as a reference in another class creates a "has a" relationship between objects |
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returning reference variables to private fields |
avoid returning reference to private data elements returning references to private data objects will allow any object that receives the reference to modify the variable |
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null references |
a reference variable that points to nothing and no operations can be performed on it references can be tested to see if they point to this prior to use |
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this reference |
reference that is a name that an object can use to itself and can be used to overcome shadowing and allow a parameter to have the same name as an instance field
can be used to call a constructor from another constructor
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enumerated types |
specialized class
known as enum, requires declaration and definition like a class
enum typename( one or more enum constants) |
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enumerated types - methods |
toString
ordinal
equals
comareTo |
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toString |
returns name of calling constant |
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ordinal |
returns the zero-based position of the constant in the enum. |
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equals |
accepts an object as an argument and returns true if the statement is equal to the calling enum constant |
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comparTo |
accepts an object as an argument and returns a negative integer if the calling constant's ordinal<than the argument's ordinal, a positive integer if the calling constant's ordinal >than the argument's ordinal and zero if the calling constants ordinal == the argument's ordinal |
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switching |
allows you to test an enum constant with a switch statement |
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garbage collection |
when objects are no longer needed, they are destroyed, freeing up memory they consumed java handles all memory operations set the reference to null and java will reclaim memory
the JVM has a process that runs in the background that reclaims memory from released objects will reclaim memory from any object that no longer has a valid reference pointing to it
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finalize method |
will run just prior to the garbage collector reclaiming its memory the garbage collector is a background thread that runs periodically it cannot be determined when the method will actually run |
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class collaboration |
two classes ineract with each other an object must know something about the second object's methods and to call them
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CRC cards |
Class, Responsibilities, and Collaborations cards are useful for determining and documenting a class's responsibilities
things a class is responsible for doing and knowing |
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primitive data types |
not created from classes
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wrapper class |
provided for all primitive data types and is a class that wraps around a primitive data type part of the java.lang so no import statement is needed to use them
this class allows you to create objects to represent a primitive data types they are immutable(cannot be changed) to get the value stored in an object, you must call a method wrapper classes provide static methods that are very useful
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Character Class |
is a wrapper class for the char data type, provides numerous methods for testing and converting character data allows a char data type to be wrapped in an object
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static character class methods |
1. isDigit 2. isLetter 3. LetterorDigit 4. isLowerCase 5. isUpperCase 6. isSpaceChar 7. isWhiteSpace |
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Substrings |
used to refer to a string that is part of another string |
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startWith/ endsWith method |
determines whether a string begins with a specified substring. is a case sensitive comparison |
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regionMatches method |
determines whether specified regions of two strings match |
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index of/last index of methods |
locates the position of the substring will return the location of a substring or character in the calling String object |
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extracting substrings |
allows you to retrieve a substring from a string |
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substring method |
returns a copy of a substring from a calling object..... two methods 1. accepts an int argument that is the starting position of the substring 2. accepts two int arguments. the first specifies the substring's starting position and the second specifies the substring's ending position
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getChars method |
stores a substring in a char array |
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toCharArray |
returns the string objects contents in an array of char values
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extracting characters to arrays |
the String class provides method to extract substrings in a String object and store them in char arrays |
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returning modified Strings |
the String class provides methods to return modified String objects |
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concat |
returns a String object that is the concatenation of two String objects |
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replace |
returns a String object with all occurrences of one character being replaced by another character |
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trim |
returns a String object with all leading and trailing whitespace characters removed |
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valueOf methods |
accepts a value of any primitive data type as its arguments and returns a string representation of the value |
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StringBuilder class |
similar to the String class except you may change the contents of StringBuilder objects A StringBuilder object can grow or shrink in size as needed to accomodate the changes |
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StringBuilder append method |
The StringBuilder class has several overloaded versions of this method which accepts an argument of any primitive data type, char array, or string object. |
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StringBuilder insert methods |
StringBuilder has several overloaded version of this method which insert a value in the calling objects string. This method accepts two arguments: 1. int specifying the position in the calling method 2. value inserted |
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StringBuilder replace method |
replaces a specified substring with a string |
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StringBuilder delete, deleteCharAt, and setCharAt methods |
used to delete a substring or a character from a StringBuilder object |
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StringBuilder toString method |
method used to convery StringBuilder object to a regular String |
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StringTokenizer class |
breaks a string down into its components called tokens provided by java api so an import statement mus be used |
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Tokens |
series of words or other items of data seprated by spaces or other characters |
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delimeter |
character that separates tokens white spaces are used by default for this |
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tokenizing |
process of breaking a sting into tokens is known as tokenizing
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non-default delimiters |
the string class trim method should be used on user input strings to avoid having whitespace become part of the last token |
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multiple delimiters |
to extract the tokens from the string, we must specify both characters as delimiters to the constructor |
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String class split method |
Tokenizes a String object and returns an array of String objects |
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numeric data type wrappers |
Java provides wrapper classes for all of the primitive data types |
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creating a wrapper object |
pass a value to the constructor and assign a primitive value to a wrapper class object |
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parse methods |
each of the numeric wrapper classes has a static method that converts a string to a number this method throws a NumberFormatException if the String object does not represent a numeric value
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wrapper class toString method |
wrapper class static method that converts a number to a String The method accepts the numbers as its argument and returns a string representation of that number |
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wrapper class toBinaryString, toHexString, and toOctalString methods |
accept an int or long as an argument and convert them to binary, hexadecimal, or octal |
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min_value and max_value |
the numeric wrapper classes each have a set of final variables which hold the minimum and maximum values for a particular data type |
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autoboxing |
process of automatically boxing up a value inside an object will allow you to use ArrayLists with primitives which would otherwise only work with objects |
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unboxing |
process of converting a wrapper class object to a primitive data type will allow you to use ArrayLists with primitives which would otherwise only work with objects |
