Transcript Package - Study Channel

Package and Some Classes
Declaration of Package
Usage of Package
Package of Java Language
What is Package ?

Way to group a related class and interface into
one unit

To resolve the name conflicts between class
names
Declaration of Package
package PackageName ;

Declare at the beginning of source file

[Print1.java], [Print2.java]
MyTest
Prints
Print1.class
Print2.class
Usage of Package

Use of absolute path name


Declare to describe the full package name
To resolve conflicts between class names
MyTest.Prints.Print1 m1;
MyTest.Prints.Print2 m2;

[AbsolutePath.java]
Use of import Statement
import packageName.className ;

Include all the classes in package

import packageName.*;
import MyTest.Prints.*;

[ImportTest.java]
java.lang Package

Basic class to enlarge the function of Java

Provide classes according to primitive type
(wrapper class)

Integer class, Double class,. ..
java.lang Class
Object
Wrapper Class
Number
System
Character
Integer
Boolean
Long
Float
Double
String
StringBuffer
Object Class



Super class of all classes
All classes are to inherit the methods of Object class
Method


Object clone() : To copy the object equally
boolean equals(Object obj) :




int hashCode() : Calculate the hash code value of the object
Class getClass() : To get Class object corresponding to object
String toString() : Convert the object into string


Compare the object as parameter with the object which calls this method
[Ex 8.5]
wait(), notify() : To control the status of thread
Wrapper Class
Classes correspond to primitive type
 int -> Integer, char -> Character, double -> Double


Reasons


Role of home for constants and methods for each type
When we need to deal with primitive type as object
Number Class
Abstract Class
 Super Class of Integer, Long, Float, Double


Method

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
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abstract int intValue() : Convert into int type
abstract long longValue() : Convert into long type
abstract float floatValue() : Convert into float type
abstract double doubleValue() : Convert into double type
Integer Class

Constant



public static final int MAX_VALUE = 2147483647
public static final int MIN_VALUE = -2147483648
Method

static int parseInt(String s) :


static int parseInt(String s , int radix) :


Convert a number in String into int type with radix
static String toBinaryString(int i) :


Convert a Number in String into int type
Convert into binary string form
static String toHexString(int i) :

Convert into hexadecimal string form
Integer Class

[IntegerClass.java]
Interger.parseInt(s);
Interger.toBinaryString(i);
...
As it is static
method...
Double Class

Constant





public static final double MAX_VALUE
=1.79769313486231570e+308
public static final double MIN_VALUE =
4.94065645841246544e-308
public static final double NaN = 0.0 / 0.0
public static final double NEGATIVE_INFINITY = -1.0 / 0.0
public static final double POSITIVE_INFINITY = 1.0 / 0.0
Double Class

the parameter is NaN or not.

static boolean isInfinite(double v) :



static Double valueOf(String s) : Method
static long doubleToLongBits(double value) :


Check whether the parameter is infinite or not.
Convert the bits represented by double type into long type bit
pattern
static boolean isNaN(double v) :
Check whether
 Convert String into Double type

Boolean Class

Constant



public static final Boolean TRUE = new Boolean(true)
public static final Boolean FALSE = new Boolean(false)
Method
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Boolean(boolean b) :

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Boolean(String s) :

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Return the boolean value of object
static boolean getBoolean(String name) :


Constructor to receive the string value "true“ or "false“
boolean booleanValue() :


Constructor to create boolean object receiving the initial value b
Return the boolean value of system attribute
static Boolean valueOf(String s) :

Return the Boolean value correspond to string s
Character Class

Constant





public static final int MAX_RADIX = 36
public static final char MAX_VALUE =‘\ffff’
public static final int MIN_RADIX = 2
public static final char MIN_VALUE =’\0000’
Method

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Character(char value) : Constructor to initialize the object as value
char charValue() : Convert into char type
static boolean isDigit(char ch) : Test whether is digit?
static boolean isLetter(char ch) : Test whether is letter?
static boolean isLetterOrDigit(char ch) : Return when it is letter or
digit.

[CharacterClass.java]
String Class

Method

char charAt(int index) :


int length() :


Convert the string into lower character
String trim() :

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Convert the string into upper character
String toLowerCase() :


Return the length of string
String toUpperCase() :


Return the character at specific position in string
Remove the white space before/after string
String substring(int beginIndex) :

Make the sub string from beginIndex to the end of the string
StringBuffer Class
Provide the string sequence operation
 Method


StringBuffer append(Type obj) :


Append the obj(to be changed into string) to string
StringBuffer insert(int offset, Type obj) :

Insert obj(to be changed into string) into specified position
Object
boolean
long
String
char
float
char[]
int
double
StringBuffer Class
String now = new java.util.Date().toString();
StringBuffer strbuf = new StringBuffer(now);
strbuf.append(" : ").append(now.length).append('.');
System.out.println(strbuf.toString());
System Class



Class for Java Virtual Machine and the control and
security for OS system
Define the standard input and output
Field
 public static InputStream in :


public static PrintStream out :


Stream to read data from standard input device
Stream to output data to standard output device
public static PrintStream err :

Standard Error Stream to output error message
Java.util.vector
We will be creating an object of Vector class and
performs various operation like adding, removing etc.
 Vector class extendsAbstractList and
implements List, RandomAccess, Cloneable,
Serializable.
 The size of a vector increase and decrease
according to the program.
 Vector is synchronized.

Methods in Vector
add(Object o): It adds the element in the end
of the Vector
 size(): It gives the number of element in the
vector.
 elementAt(int index): It returns the element
at the specified index.
 firstElement(): It returns the first element of
the vector.
 lastElement(): It returns last element.
 removeElementAt(int index): It deletes the
element from the given index.

Methods in Vector class
elements(): It returns an enumeration of the
element
 In this example we have also
used Enumeration interface to retrieve the
value of a vector. Enumerationinterface has
two methods.
 hasMoreElements(): It checks if this
enumeration contains more elements or not.
 nextElement(): It checks the next element of
the enumeration.

import java.util.*;
public class VectorDemo{
public static void main(String[] args){
Vector<Object> vector = new Vector<Object>();
int primitiveType = 10;
Integer wrapperType = new Integer(20);
String str = "tapan joshi";
vector.add(primitiveType);
vector.add(wrapperType);
vector.add(str);
vector.add(2, new Integer(30));
System.out.println("the elements of vector: " + vector);
System.out.println("The size of vector are: " + vector.size());
System.out.println("The elements at position 2 is: " + vector.elementAt(2));
System.out.println("The first element of vector is: " + vector.firstElement());
System.out.println("The last element of vector is: " + vector.lastElement());
vector.removeElementAt(2);
Enumeration e=vector.elements();
System.out.println("The elements of vector: " + vector);
while(e.hasMoreElements()){
System.out.println("The elements are: " + e.nextElement());
}
}
}
Example on Stack class
import java.util.*;
public class StackDemo{
public static void main(String[] args) {
Stack stack=new Stack();
stack.push(new Integer(10));
stack.push("a");
System.out.println("The contents of Stack is" + stack);
System.out.println("The size of an Stack is" + stack.size());
System.out.println("The number poped out is" + stack.pop());
System.out.println("The number poped out is " + stack.pop());
//System.out.println("The number poped out is" + stack.pop());
System.out.println("The contents of stack is" + stack);
System.out.println("The size of an stack is" + stack.size());
}
}
Example on Scanner class
import java.util.Scanner;
public class ScannerDemo {
public static void main(String[] args) {
Scanner scanner = new Scanner(System.in);
// Read string input for username
System.out.print("Username: ");
String username = scanner.nextLine();
// Read string input for password
System.out.print("Password: ");
String password = scanner.nextLine();
// Read an integer input for another challenge
System.out.print("What is 2 + 2: ");
int result = scanner.nextInt();
if (username.equals("admin") && password.equals("secret") &&
result == 4) {
System.out.println("Welcome to Java Application");
} else {
System.out.println("Invalid username or password, access
denied!");
}
}
}
Example on Date Class
import java.util.*;
public class DateDemo{
public static void main(String[] args) {
Date d=new Date();
System.out.println("Today date is "+ d);
}
}
JAVA.IO
Example on File
import java.io.*;
class FileWrite
{
public static void main(String args[])
{
try{
// Create file
FileWriter fstream = new FileWriter("out.txt",true);
BufferedWriter out = new BufferedWriter(fstream);
out.write("Hello Java");
//Close the output stream
out.close();
}catch (Exception e){//Catch exception if any
System.err.println("Error: " + e.getMessage());
}
}
}
java.io.Reader class
BufferedReader class
Method
Return
Type
Description
read( )
int
Reads a single character
read(char[] cbuf, int off,
int len)
int
Read characters into a portion of an
array.
readLine( )
String
Read a line of text. A line is
considered to be terminated by ('\n').
close( )
void
Closes the opened stream.
import java.io.*;
public class ReadStandardIO{
public static void main(String[] args) throws IOException{
InputStreamReader inp = new InputStreamReader(System.in)
BufferedReader br = new BufferedReader(inp);
System.out.println("Enter text : ");
String str = in.readLine();
System.out.println("You entered String : ");
System.out.println(str);
}
}