Built in packages & String Class

    Java contains plenty of built in packages. A package is similar to the header file in ‘C’ and ‘C++’. They contain a host of built in classes and interfaces. To include a built in package into your program you can use the ‘ import’.

General format: import package_name;

Examples:

1. import java.lang.*; imports all the classes from the package “java.lang”.
2. import java.lang.string; imports just class string from the package “java lang”.

---

java.lang

---

1. String class: Allows you to manipulate with strings in java.
   
   Constructors:
   
   1. String();   Construct an empty string object.
   2. String(char array[]);   Constructs a string object for the contents of a character array.
   3. String(char array[], int start_index, int numchars);   Constructs a string object from the partial contents of a character array.
   4. String(String str);   Constructs a string object from another string object.

import java.lang.*;
class App30
{
public static void main(String yck[])
{
String s1=new String();
char x[]={'C','H','A','I','T','A','N','Y','A'};
String s2=new String(x);
String s3=new String(x,2,5);
String s4=new String(s2);
System.out.println(s1);
System.out.println(s2);
System.out.println(s3);
System.out.println(s4);
}
}


output:

\>javac App30.java
\>java App30
CHAITANYA
AITAN
CHAITANYA

Methods:

1. int length(); Returns the length of the string.

import java.lang.*;
class App31
{
public static void main(String yck[])
{
String s=new String("CHAITANYA");
int len;
len=s.length();
System.out.println("Length of the String is = "+len);
}
}


output:

\>javac App31.java
\>java App31
Length of the String is = 9

char charAt(int where); Returns the character at a specified position.

import java.lang.*;
class App32
{
public static void main(String yck[])
{
String s=new String("CHAITANYA");
char ch=s.charAt(2);
System.out.println(ch);
}
}


output:

\>javac App32.java
\>java App32
A

void getChars(int startindex, int endindex, char target[], int targetindex); construct a character array from the contents of a string object.

Example:

import java.lang.*;
class App33
{
public static void main(String yck[])
{
String s=new String("CHAITANYA");
char x[]=new char[s.length()];
s.getChars(0,3,x,3);
System.out.println(s);
for(int i=0;i System.out.println(x[i]);
}
}


output:

\>javac App33.java
\>java App33
CHAITANYA



C
H
A

char[] toCharArray(); Converts the contents of the entire string object into a character array.

import java.lang.*;
class App34
{
public static void main(String yck[])
{
String s=new String("CHAITANYA");
char x[]=s.toCharArray();
System.out.println(s);
System.out.println(x);
for(int i=0;i System.out.println(x[i]);
}
}


output:

\>javac App34.java
\>java App34
CHAITANYA
CHAITANYA
C
H
A
I
T
A
N
Y
A