String Handling & Wrapper Classes

StringTokenizer:
It allows an application to break a string into tokens(words).

Example:
"Welcome to Java" is a one string and it has 3 tokens(words).

java.util.StringTokenizer 

Constructor:
  public StringTokenizer(String);

Methods:
  public boolean hasMoreTokens();
=>It returns true if the token is present, otherwise returns false
  public String nextToken();
=>It returns current token and moves the cursor to next token.
  public int countTokens();
=>It returns no. of tokens.

Program to count the no. of words:

import java.util.*;

class Demo
{
public static void main(String args[])
{
String s="Welcome to Sathya Technologies";
StringTokenizer st=new StringTokenizer(s);
int n=st.countTokens();
System.out.println(n);
}
}
Program to iterate word by word in a given string:

import java.util.*;

class Demo
{
public static void main(String args[])
{
String s="Welcome to Sathya Technologies";
StringTokenizer st=new StringTokenizer(s);
while(st.hasMoreTokens())
{
System.out.println(st.nextToken());
}
}

}

Command Line Arguments:

Ø The arguments that are passed at the command prompt are called command line arguments.

Ø Command line arguments are received by main method only.

Ø The arguments are received string format only.

Examples:

1)  class Demo

{

                  public static void main(String args[])

                  {

                          for(String s : args)

                          {

                                   System.out.println(s);

}

}

}

2)  class Demo

{

                  public static void main(String args[])

{

                  System.out.println(args[0]+args[1]);

}

}

To run the above application:

C:\> java Demo Taj Mahal

Output: TajMahal

C:\> java Demo 10 20

Output: 1020 because command line arguments are received as a string format only.

To convert string format to other formats we need wrapper classes.

Wrapper Classes:

Each of Java’s 8 primitive data types has a class and those classes are called wrapper classes because they wrap the data into an object.

List of primitive data types:

1)  byte 2) short 3) int 4) long 5) float 6) double 7) char 8) boolean

List of wrapper classes:

1)  Byte 2) Short 3) Integer 4) Long 5) Float 6) Double 7) Character 8) Boolean

Example:

class Demo

{

         public static void main(String args[])

{

         int x=Integer.parseInt(args[0]);

         int y=Integer.parseInt(args[1]);

         System.out.println(x+y);

}

}

To run the above application:

C:\> java Demo 10 20

Output: 30

To covert primitive type to reference type

int a=5;

Integer i=new Integer(a);

To covert reference type to primitive type:

Integer i=new Integer(5);

int x=i.intValue();

Auto boxing:

The process of converting primitive type to the corresponding reference type is known as auto boxing.

Example:

int x=5;

Integer i=x; => It is called as auto boxing

Auto unboxing:

The process of converting reference type to the corresponding primitive type is known as auto unboxing.

Example:

Integer i=new Integer(5);

int x=i; => it is called as auto unboxing.

Both auto boxing and auto unboxing features are introduced in JDK 1.5 verion in 2004.

Assignment1:

1) Write a program to convert byte array into a String and display by using the following constructor of String class:

         public String(byte[]);

2) Write a program to convert char array into a String and display by using the following constructor of String class:

         public String(char[]);

3) Write a program to convert String into a byte array and display by using the following method of String class:

         public byte[] getBytes();

4) Write a program to convert String into a char array and display by using the following method of String class:

         public char[] toCharaArray();

5) Write a program to concatinate two strings by using the following method:

         public String concat(String);

Assignment2:
1) Write a program to check whether given file is java file or not by using the following method of String class.
         public boolean endsWith(String);
2) Write a program to check whether given string starts with alphabet A or not by using the following method of String class.
         public boolean startsWith(String);
3) Write a program to count the no. of words in a given string by using the following constructor & method.
         public StringTokenizer(String);
         public int countTokens();
4) Write a program to iterate word by word in a given string by using the following constructor & methods.
         public StringTokenizer();
         public boolean hasMoreTokens();
         public String nextToken();