important classes in java
DESCRIPTION
Min Chen School of Computer Science and Engineering Seoul National University. Data Structure: Java Programming 2. Important Classes in java. Content. Inheritance implementation in Java Important Classes in Java Object Class Integer Class String Class StringTokenizer Class - PowerPoint PPT PresentationTRANSCRIPT
IMPORTANT CLASSES IN JAVA
Data Structure: Java Programming 2
Min ChenSchool of Computer Science and Engineering
Seoul National University
Content
Inheritance implementation in Java Important Classes in Java
Object Class Integer Class String Class StringTokenizer Class ArrayList Class
Inheritance in Java
Example: An inheritance implementation
CEOsCompanyProducts
SportsmenEmployer
SportsLeague
StarsSchoolDrama
PeopleName
GenderAge
Place of Birth
People Class•Attributes• Name• Gender• Age• Place of Birth
•Methods• getName()• …
CEOs Class•Attributes• Company• Products
•Methods• getCompany()• …
People Class
Definition of Attributes
Definition of Methods
Constructed function
Necessary if you defined your own constructed function and
the class will be inherited.
CEO Class
Definition of Attributes
Definition of Methods
Constructed function
Modified HelloWorld Class
Hello World in Java!My name is Steve Jobs.My company is Apple.
Important classes in Java
Why java is so popular? Write Once, Run Everywhere Easy to Lean Easy to Use
Standard and Efficient Package Library!
Some Essential Classes in Java will make your programming much easier!
Concept of Package
In Java, a set of essential Classes with related characteristics are packed in packages
How to use a package?
How to create a package?
import java.util.*;
package mypackage;
Object Class
The MOTHER Class of the Java World All Classes in Java are subclass of Object
Class Extends the Object Class is default Unnecessary to declare when define a new
Class The methods in Object Class can be inherited
in all of the classes clone() equals() toString()
ClassName+@+hashCode
equals() in Object Class
Compare two objects When the two objects are actually one
instance, return true Else, return false
CEO steve=new CEO("Jobs","Male",54,"U.S.","Apple Inc.","Mac..."); CEO jobs=steve; CEO bill=new CEO("Jobs","Male",54,"U.S.","Apple Inc.","Mac...");
steve.equals(bill);Return false
steve.equals(jobs);Return true
Integer Class
Be Used To Define a integer Constructed Function
Integer(int) Integer(String)
Important Methods parseInt(String) toString()
Integer myInt = new Integer(“321”);
Integer myInt = Integer.parseInt(“321”);
String myStr = myInt.toString();
Static Method in Class
A static method can be called without creating the instance of the class
Integer myInt = Integer.parseInt(“321”);
public class Integer { …
public static Integer parseInt ( String ) { … } … }
String Class
Construct Function String( char[] )
Important Methods equals() toLowerCase() & toUpperCase() indexOf (String s) replace(char old ,char new) substring(int start ,int end) charAt (int index) getChars(int start,int end,char c[],int offset )
equals() in String Class
Has been overwritten Be used to compare the values of
two strings String a=“A String”; String b=“A String”; String c= “a string”
a.equals(b)Return true
a.equlas(c) Return false a. equalsIgnoreCase(c) Return true
StringTokenizer Class
Problem: How can we retrieval words from a
sentence? Example:
StringTokenizer Class address this problem Divide the sentence into tokens Retrieval words by the tokens
You adore the light, so you will never fear the darkness.
StringTokenizer Class(cont.) Defined in the package of java.utils Constructed Function
StringTokenizer( String text ) StringTokenizer( String text, String
delimiter ) Important Methods
boolean hasMoreTokens() String nextToken() int countTokens()
Provide a rule of dividing string
Divide the string by blanks
StringTokenizer Class(cont.)
Create two StringTokenizer instances for
the textLoop to print
out the tokens we can get
Import the package
ArrayList Class
Typical Features of Array Same Data Type Predefined Array Length
ArrayList Provide functionality of array Support different data type in one array Flexible Array Length
ArrayList Class(cont.)
Important Methods add(object o) & add(int index, object o)
Add a data into the ArrayList get(int index)
Retrieval a data from the ArrayList indexOf()
Search for the item Remove()
Remove a corresponding index or a value isEmpty()
ArrayList Class(cont.)Import the package
Create an instance of Array List
Add items to the ArrayList
Insert 23 into the index of 1Get items from
index
Search a predicted value
from the arraylist
Remove a predicted value
Result: Obama 23 0 steve is in the index of [3]
ArrayList Class(cont.)
Warning Message for ArrayList Type safety: The method add(Object)
belongs to the raw type ArrayList. References to generic type ArrayList<E> should be parameterized
The data type of the item we retrieval from the ArrayList is Object A transform is necessary
How to define a Type-Restricted ArrayList? ArrayList<String> myArr = new
ArrayList<String> ();
Thank you