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import Vehicle;
public class Car extends Vehicle{
public int DoorNum = 4 ;
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import java.io.*;
import Car;
public class Me{
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Car mycar = new Car();
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}
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Circle
radius
findArea
circle1: Circle
radius = 2
new Circle()
circlen: Circle
radius = 5
new Circle()
...
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notation for
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class Circle
{
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double findArea()
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class Car {
int color_number;
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int speed;
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void speedUp() {…};
void slowDown() { … }
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5.4 `￥
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2
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ClassName objectName;
Example: Car myCar;
Circle myCircle;
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Example: myCar = new Car();
myCircle = new Circle();
`￥
2
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ClassName objectName = new ClassName();
Example:
Car myCar = new Car();
Circle myCircle = new Circle();
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instantiate
instantiate
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2
5
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numOfObjects
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variable, and
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class variable
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underline: static variables or metods
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private double radius
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public static int getNumOfObjects( )
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TestInstanceAndClassVariable Run
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class Tom{
int x=98,y;
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}
}
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Example 5.6
P¨ this? super
class B extends A {
int b, c;
B() {
this(2, 3);
}
B(int new_b, int new_c)
{
super(1);
b = new_b;
c = new_c;
}
}
class A {
int a;
A(int new_value) {
a = new_value;
}
}
class Demo {
public static void main(String[] args) {
B obj_b = new B();
System.out.println("a= "+obj_b.a + "; b= "+obj_b.b +
"; c= "+ obj_b.c);
}
}
?2T a= 1; b= 2; c= 3
5.13 `1"s
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5.13.1 1 ó
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5.13.1 1 ó
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Example 5.6 ·?~ {
μ
t
1
Name
1
Borrower
Address
Mortgage
1
1
Example 5.6 ·?~ {
The following is a test program that uses
the classes Name, Address, Borrower,
and Mortgage.
Run
BorrowMortgage
5.15 Java API and Core Java classes
)java.lang
Contains core Java classes, such as numeric
classes, strings, and objects. This package is
implicitly imported to every Java program.
)java.awt
Contains classes for graphics.
)java.applet
Contains classes for supporting applets.
5.15 Java API and Core Java classes, cont.
)java.io
Contains classes for input and output
streams and files.
)java.util
Contains many utilities, such as date.
)java.net
Contains classes for supporting
network communications.
5.15 Java API and Core Java classes, cont.
)java.awt.image
Contains classes for managing bitmap
images.
)java.awt.peer
Platform-specific GUI implementation.
)Others:
java.sql
java.rmi
5.16 The String Class
)Declaring a String:
–String message = "Welcome to Java!"
–String message = new
String("Welcome to Java!“);
–String s = new String();
)String 1?
)String ?¤
)01
)String Length
)_
ì String?￥3?
String 1?
)equals
String s1 = "Welcome";
String s2 = "welcome";
if (s1.equals(s2))
{ ... }
if (s1 == s2)
{
…
}
01
String is an immutable class; its values
cannot be changed individually.
String s1 = "Welcome to Java";
String s2 = s1.substring(0,10) + "HTML";
Finding String Length
Finding string length using the length()
method:
message = "Welcome";
message.length() (returns 7)
Retrieving Individual
Characters in a String
)Do not use message[0]
)Use message.charAt(index)
)Index starts from 0
5.17 The StringBuffer Class
StringBuffer ?
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StringBuffer Constructors
)public StringBuffer()
No characters, initial capacity 16 characters.
)public StringBuffer(int length)
No characters, initial capacity specified by the
length argument.
)public StringBuffer(String str)
Represents the same sequence of characters
as the string argument. Initial capacity 16
plus the length of the string argument.
Appending New Contents
into a String Buffer
StringBuffer strBuf = new
StringBuffer();
strBuf.append("Welcome");
strBuf.append(' ');
strBuf.append("to");
strBuf.append(' ');
strBuf.append("Java");
5.18 The StringTokenizer
Class Constructors
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)StringTokenizer(String s, String
delim, boolean returnTokens)
)StringTokenizer(String s, String
delim)
)StringTokenizer(String s)
The StringTokenizer Class
Methods
)boolean hasMoreTokens()
)String nextToken()
)String nextToken(String delim)
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