Package and Some Classes

1
Package and Some Classes
Declaration of Package Usage of Package Package
of Java Language
2
What is Package ?

• Way to group a related class and interface into
  one unit
• To resolve the name conflicts between class names
  

3
Declaration of Package
package PackageName

• Declare at the beginning of source file
• Print1.java, Print2.java

4
Usage of Package

• Use of absolute path name
• Declare to describe the full package name
• To resolve conflicts between class names
• AbsolutePath.java

MyTest.Prints.Print1 m1
MyTest.Prints.Print2 m2
5
Use of import Statement
import packageName.className

• Include all the classes in package
• import packageName.
• ImportTest.java

import MyTest.Prints.
6
java.lang Package

• Basic class to enlarge the function of Java
• Provide classes according to primitive type
  (wrapper class)
• Integer class, Double class,. ..

7
java.lang Class
Wrapper Class
8
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)
• Compare the object as parameter with the object
  which calls this method
• 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
• Ex 8.5
• wait(), notify() To control the status of
  thread

9
Wrapper Class

• Classes correspond to primitive type
• int -gt Integer, char -gt Character, double -gt
  Double
• Reasons
• Role of home for constants and methods for each
  type
• When we need to deal with primitive type as
  object

10
Number Class

• Abstract Class
• Super Class of Integer, Long, Float, Double
• Method
• 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

11
Integer Class

• Constant
• public static final int MAX_VALUE 2147483647
• public static final int MIN_VALUE -2147483648
• Method
• static int parseInt(String s)
• Convert a Number in String into int type
• static int parseInt(String s , int radix)
• Convert a number in String into int type with
  radix
• static String toBinaryString(int i)
• Convert into binary string form
• static String toHexString(int i)
• Convert into hexadecimal string form

12
Interger Class

• IntegerClass.java

As it is static method...
Interger.parseInt(s) Interger.toBinaryString(
i) . . .
13
Double Class

• Constant
• public static final double MAX_VALUE
  1.79769313486231570e308
• 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

14
Double Class

• Method
• static long doubleToLongBits(double value)
• Convert the bits represented by double type into
  long type bit pattern
• static boolean isNaN(double v)
• Check whether the parameter is NaN or not.
• static boolean isInfinite(double v)
• Check whether the parameter is infinite or not.
• static Double valueOf(String s)
• Convert String into Double type

15
Boolean Class

• Constant
• public static final Boolean TRUE new
  Boolean(true)
• public static final Boolean FALSE new
  Boolean(false)
• Method
• Boolean(boolean b)
• Constructor to create boolean object receiving
  the initial value b
• Boolean(String s)
• Constructor to receive the string value "true or
  "false
• boolean booleanValue()
• Return the boolean value of object
• static boolean getBoolean(String name)
• Return the boolean value of system attribute
• static Boolean valueOf(String s)
• Return the Boolean value correspond to string s

16
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
• 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

17
String Class

• Method
• char charAt(int index)
• Return the character at specific position in
  string
• int length()
• Return the length of string
• String toUpperCase()
• Convert the string into upper character
• String toLowerCase()
• Convert the string into lower character
• String trim()
• Remove the white space before/after string
• String substring(int beginIndex)
• Make the sub string from beginIndex to the end of
  the string

18
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 String char boolean char int
long float double
19
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())
20
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
• Stream to read data from standard input device
• public static PrintStream out
• Stream to output data to standard output device
• public static PrintStream err
• Standard Error Stream to output error message