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5 Strings — Java Programming

5.1. Introduction

Strings play an important role in Java programming. Let us explore various classes and functions related to Strings.

5.2 Strings

A string is an array of characters. We can define string as below:

char chars[] = {'a','b','c'};

A string has a fixed number of characters. In Java, a string is an object of the class, which belongs to java.lang package. The string class is available to all classes by default. String objects are immutable- that is once the object is created, the contents cannot be changed. A variable declared as a String reference can be changed to point at some other String object at any time.

For example:

String str=”this is an example”;

System.out.println(str);

Constructor is used as in the statement String s=new String();

String belong to the package java.lang.String

5.2.1 Different ways of calling the String constructor

String Constructor

Description

public String();

Instantiating a String object.

public String(char value[]);

Give a character array.

public String(char value[], int offset, int count);

Get the substring starting from offset count number of chars.

public String(String value);

Directly give the string constant as the parameter.

5.2.2 Methods of String class

Method

Description

public int length();

Returns the length of the String.

public char charAt(int index)

Return the character at the specified index

public int indexOf(int ch)

public int indexOf(int ch, int fromindex)

public indexOf(String s)

public indexOf(string s, int f)

Returns the index of the first occurrence of the character, ch. If unsuccessful returns -1

Returns the first occurrence of the character, ch, that is greater than or equal to from index, if not successful return -1.

Returns index of the first of the first occurrence of the specified string

Returns index of the first occurrence of the specified string.

public int lastIndexOf(int ch)

public int lastIndexOf(int c, int f)

public int lastIndexOf(String s)

public int lastIndexOf(String s,int f)

Returns the index of the last occurrence of the specified character, ch. If Unsuccessful -1 is returned

Return the last occurrence from the specified index, if unsuccessful returns -1.

Returns the index of the last occurrence of the specified string.

Returns the index of last occurrence of the specified string.

public string substring(int beginIndex, int endIndex)

Create and returns a new string that is a sub string from the specified beginIndex to the specified endindex.

public boolean equals(object obj)

The result is true if the argument is not null and is string object that represents the same sequence of characters as this object obj.

public String replace(char oldch, char newch)

Returns a new string resulting from replacing all occurrences of oldch in this string with newch.

public Boolean startsWith(String prefix)

Return true if the character sequence represented by the argument is a prefix of the character sequence

public Boolean startsWith(string prefix, int offset)

Return true if the character sequence represented by the argument is a prefix of the substring of this object starting at index offset, returns false otherwise.

public String toLowerCase()

Converts a string to lowercase.

public String toString()

This object that is already a string is returned.

public String t8oUppercase()

Converts a string to uppercase.

public String trim()

Removes white spaces from both ends of a string.

public static String valueof(Boolean b)

Creates the string representation of the Boolean argument.

public static String valueOf(char c)

Creates the string representation of the char argument.

5.3 String buffers

The String class provides many capabilities for manipulating strings.

Unlike String objects, stringBuffer objects are modifiable.

For example

StringBuffer st;

st=new StringBuffer(10);

Also there is flexibility, if the number of characters is more than specified, then automatically the string buffer expands to accommodate those extra characters.

5.3.1 The methods of string buffer

public StringBuffer append(char c)

Appends the string representation of the char argument to this StringBuffer object

public int capacity()

Returns the current capacity of this StringBuffer object

public char charAt(int index)

Determines the character at a specific index in this StringBuffer object

public void getChar(int srcbegin, int srcend, char dest[], int destBegin)

Characters are copied from this StringBuffer object into the destination character array dest.

public StringBuffer insert(int offset, char c)

Inserts the string representation of the char argument into the StringBuffer object

public StringBuffer insert(int offset, char str[])

Inserts the string representation of the char array argument into this StringBuffer object

public int length()

Returns the number of characters in the StringBuffer object

public StringBuffer reverse()

The reverse of the sequence replaces the character sequence contained in this StringBuffer.

public void setcharAt(int index, char ch)

The character at the specified index of this string buffer is set to ch.

public string toString()

A new string object is allocated and initialized to contain the character sequence currently represented by the StringBuffer object.

Program 5.1. To find the length of a given string using a custom defined function

//strlen.java
//click here for code
import java.lang.*;
class len{
 public static int findlen(String s){
  int i,length;
  length=s.length();
 return length;
}
}
class strlen{
public static void main(String args[]){
StringBuffer s =new StringBuffer("finding my length?");
System.out.println(len.findlen(s.toString()));
}
}
// Output:
18

Program 5.2 Program to reverse a string using custom define function

//reversing.java
//click here for code
import java.lang.*;
class rev{
public static String reverse(String s){
int i,length;
length=s.length();
StringBuffer revst = new StringBuffer(length);
for(i=length-1;i>=0;i--)
{
revst.append(s.charAt(i));
}
return revst.toString();
}
}

class reversing{
public static void main(String args[])
{
StringBuffer s = new StringBuffer("I am getting reversed");
System.out.println(rev.reverse(s.toString()));
}
}
/*Output:
desrever gnitteg ma I
*/

Program 5.3 Program to sort a set of strings

//sortStrings.java

//Click here for code

import java.io.*;
public class sortStrings{
public static void main(String args[])
{
int n=0;
String ns;
String name[];
name=new String[20];
try{
DataInputStream in;
in=new DataInputStream(System.in);
System.out.println("enter value for n");
System.out.flush();
ns=in.readLine();
n=Integer.parseInt(ns);
System.out.println("enter the names");
System.out.flush();
for(int i=0;i<n;i++)
{
System.out.flush();
name[i]=in.readLine();
}
for(int i=0;i<n-1;i++)
for(int j=i+1;j<n;j++)
{
String t;
if(name[i].compareTo(name[j])<0)
{
t=name[i];
name[i]=name[j];
name[j]=t;
}
}
}
catch(Exception e)
{
System.out.println("IO error");
System.exit(1);
}
System.out.println("sorted names");
for(int i=0;i<n;i++)
{
System.out.println(name[i]);
}
}
}
/* Output:
enter value for n
2
enter the names
program
java
sorted names
program
java
*/

5.4 Summary

In this chapter you have been introduced with strings and string buffers.

License

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Java Programming Copyright © by Valli Kumari Vatsavayi and KBS Phanindra Varma is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License, except where otherwise noted.

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