The string is a sequence of characters. In Java, objects of String are immutable which means a constant and cannot be changed once created.
Creating a String
There are two ways to create string in Java:
1. String literal
String s = “GeeksforGeeks”;
2. Using new keyword
String s = new String (“GeeksforGeeks”);
String Constructors in Java
1. String(byte[] byte_arr)
Construct a new String by decoding the byte array. It uses the platform’s default character set for decoding.
Example:
byte[] b_arr = {71, 101, 101, 107, 115};
String s_byte =new String(b_arr); //Geeks
2. String(byte[] byte_arr, Charset char_set)
Construct a new String by decoding the byte array. It uses the char_set for decoding.
Example:
byte[] b_arr = {71, 101, 101, 107, 115};
Charset cs = Charset.defaultCharset();
String s_byte_char = new String(b_arr, cs); //Geeks
3. String(byte[] byte_arr, String char_set_name)
Construct a new String by decoding the byte array. It uses the char_set_name for decoding. It looks similar to the above constructs and they appear before similar functions but it takes the String(which contains char_set_name) as parameter while the above constructor takes CharSet.
Example:
byte[] b_arr = {71, 101, 101, 107, 115};
String s = new String(b_arr, "US-ASCII"); //Geeks
4. String(byte[] byte_arr, int start_index, int length)
Construct a new string from the bytes array depending on the start_index(Starting location) and length(number of characters from starting location).
Example:
byte[] b_arr = {71, 101, 101, 107, 115};
String s = new String(b_arr, 1, 3); // eek
5. String(byte[] byte_arr, int start_index, int length, Charset char_set)
Construct a new string from the bytes array depending on the start_index(Starting location) and length(number of characters from starting location).Uses char_set for decoding.
Example:
byte[] b_arr = {71, 101, 101, 107, 115};
Charset cs = Charset.defaultCharset();
String s = new String(b_arr, 1, 3, cs); // eek
6. String(byte[] byte_arr, int start_index, int length, String char_set_name)
Construct a new string from the bytes array depending on the start_index(Starting location) and length(number of characters from starting location).Uses char_set_name for decoding.
Example:
byte[] b_arr = {71, 101, 101, 107, 115};
String s = new String(b_arr, 1, 4, "US-ASCII"); // eeks
7. String(char[] char_arr)
Allocates a new String from the given Character array
Example:
char char_arr[] = {'G', 'e', 'e', 'k', 's'};
String s = new String(char_arr); //Geeks
8. String(char[] char_array, int start_index, int count)
Allocates a String from a given character array but choose count characters from the start_index.
Example:
char char_arr[] = {'G', 'e', 'e', 'k', 's'};
String s = new String(char_arr , 1, 3); //eek
9. String(int[] uni_code_points, int offset, int count)
Allocates a String from a uni_code_array but choose count characters from the start_index.
Example:
int[] uni_code = {71, 101, 101, 107, 115};
String s = new String(uni_code, 1, 3); //eek
10. String(StringBuffer s_buffer)
Allocates a new string from the string in s_buffer
Example:
StringBuffer s_buffer = new StringBuffer("Geeks");
String s = new String(s_buffer); //Geeks
11. String(StringBuilder s_builder)
Allocates a new string from the string in s_builder
Example:
StringBuilder s_builder = new StringBuilder("Geeks");
String s = new String(s_builder); //Geeks
String Methods in Java
Returns the number of characters in the String.
"GeeksforGeeks".length(); // returns 13
Returns the character at ith index.
"GeeksforGeeks".charAt(3); // returns ‘k’
Return the substring from the ith index character to end.
"GeeksforGeeks".substring(3); // returns “ksforGeeks”
Returns the substring from i to j-1 index.
"GeeksforGeeks".substring(2, 5); // returns “eks”
Concatenates specified string to the end of this string.
String s1 = ”Geeks”;
String s2 = ”forGeeks”;
String output = s1.concat(s2); // returns “GeeksforGeeks”
Returns the index within the string of the first occurrence of the specified string.
String s = ”Learn Share Learn”;
int output = s.indexOf(“Share”); // returns 6
Returns the index within the string of the first occurrence of the specified string, starting at the specified index.
String s = ”Learn Share Learn”;
int output = s.indexOf("ea",3);// returns 13
Returns the index within the string of the last occurrence of the specified string.
String s = ”Learn Share Learn”;
int output = s.lastIndexOf("a"); // returns 14
Compares this string to the specified object.
Boolean out = “Geeks”.equals(“Geeks”); // returns true
Boolean out = “Geeks”.equals(“geeks”); // returns false
Compares string to another string, ignoring case considerations.
Boolean out= “Geeks”.equalsIgnoreCase(“Geeks”); // returns true
Boolean out = “Geeks”.equalsIgnoreCase(“geeks”); // returns true
Compares two string lexicographically.
int out = s1.compareTo(s2);
// where s1 and s2 are
// strings to be compared
This returns difference s1-s2. If :
out < 0 // s1 comes before s2
out = 0 // s1 and s2 are equal.
out > 0 // s1 comes after s2.
Compares two string lexicographically, ignoring case considerations.
int out = s1.compareToIgnoreCase(s2);
// where s1 and s2 are
// strings to be compared
This returns difference s1-s2. If :
out < 0 // s1 comes before s2
out = 0 // s1 and s2 are equal.
out > 0 // s1 comes after s2.
Note: In this case, it will not consider case of a letter (it will ignore whether it is uppercase or lowercase).
Converts all the characters in the String to lower case.
String word1 = “HeLLo”;
String word3 = word1.toLowerCase(); // returns “hello"
Converts all the characters in the String to upper case.
String word1 = “HeLLo”;
String word2 = word1.toUpperCase(); // returns “HELLO”
Returns the copy of the String, by removing whitespaces at both ends. It does not affect whitespaces in the middle.
String word1 = “ Learn Share Learn “;
String word2 = word1.trim(); // returns “Learn Share Learn”
Returns new string by replacing all occurrences of oldChar with newChar.
String s1 = “feeksforfeeks“;
String s2 = “feeksforfeeks”.replace(‘f’ ,’g’); // returns “geeksgorgeeks”
Note: s1 is still feeksforfeeks and s2 is geeksgorgeeks
Returns true if string contains contains the given string
String s1="geeksforgeeks"
String s2="geeks"
s1.contains(s2) // return true
Example of String Constructor and String Methods
Below is the implementation of the above mentioned topic:
Java
import java.io.*;
import java.util.*;
class Test
{
public static void main (String[] args)
{
String s= "GeeksforGeeks";
System.out.println("String length = " + s.length());
System.out.println("Character at 3rd position = "
+ s.charAt(3));
System.out.println("Substring " + s.substring(3));
System.out.println("Substring = " + s.substring(2,5));
String s1 = "Geeks";
String s2 = "forGeeks";
System.out.println("Concatenated string = " +
s1.concat(s2));
String s4 = "Learn Share Learn";
System.out.println("Index of Share " +
s4.indexOf("Share"));
System.out.println("Index of a = " +
s4.indexOf('a',3));
Boolean out = "Geeks".equals("geeks");
System.out.println("Checking Equality " + out);
out = "Geeks".equals("Geeks");
System.out.println("Checking Equality " + out);
out = "Geeks".equalsIgnoreCase("gEeks ");
System.out.println("Checking Equality " + out);
int out1 = s1.compareTo(s2);
System.out.println("the difference between ASCII value is="+out1);
String word1 = "GeeKyMe";
System.out.println("Changing to lower Case " +
word1.toLowerCase());
String word2 = "GeekyME";
System.out.println("Changing to UPPER Case " +
word2.toUpperCase());
String word4 = " Learn Share Learn ";
System.out.println("Trim the word " + word4.trim());
String str1 = "feeksforfeeks";
System.out.println("Original String " + str1);
String str2 = "feeksforfeeks".replace('f' ,'g') ;
System.out.println("Replaced f with g -> " + str2);
}
}
|
Output
String length = 13
Character at 3rd position = k
Substring ksforGeeks
Substring = eks
Concatenated string = GeeksforGeeks
Index of Share 6
Index of a = 8
Checking Equality false
Checking Equality ...
For Set – 2 you can refer: Java.lang.String class in Java | Set 2
This article is contributed by Rahul Agrawal. Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above
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