String class in Java
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
1. int length()
Returns the number of characters in the String.
"GeeksforGeeks".length(); // returns 13
2. Char charAt(int i)
Returns the character at ith index.
"GeeksforGeeks".charAt(3); // returns ‘k’
3. String substring (int i)
Return the substring from the ith index character to end.
"GeeksforGeeks".substring(3); // returns “ksforGeeks”
4. String substring (int i, int j)
Returns the substring from i to j-1 index.
"GeeksforGeeks".substring(2, 5); // returns “eks”
5. String concat( String str)
Concatenates specified string to the end of this string.
String s1 = ”Geeks”;
String s2 = ”forGeeks”;
String output = s1.concat(s2); // returns “GeeksforGeeks”
6. int indexOf (String s)
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
7. int indexOf (String s, int i)
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
8. Int lastIndexOf( String s)
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
9. boolean equals( Object otherObj)
Compares this string to the specified object.
Boolean out = “Geeks”.equals(“Geeks”); // returns true
Boolean out = “Geeks”.equals(“geeks”); // returns false
10. boolean equalsIgnoreCase (String anotherString)
Compares string to another string, ignoring case considerations.
Boolean out= “Geeks”.equalsIgnoreCase(“Geeks”); // returns true
Boolean out = “Geeks”.equalsIgnoreCase(“geeks”); // returns true
11. int compareTo( String anotherString)
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.
12. int compareToIgnoreCase( String anotherString)
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).
13. String toLowerCase()
Converts all the characters in the String to lower case.
String word1 = “HeLLo”;
String word3 = word1.toLowerCase(); // returns “hello"
14. String toUpperCase()
Converts all the characters in the String to upper case.
String word1 = “HeLLo”;
String word2 = word1.toUpperCase(); // returns “HELLO”
15. String trim()
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”
16. String replace (char oldChar, char newChar)
Returns new string by replacing all occurrences of oldChar with newChar.
String s1 = “feeksforfeeks“;
String s2 = “feeksforfeeks”.replace(‘f’ ,’g’); // returns “geeksforgeeks”
Note: s1 is still feeksforfeeks and s2 is geeksgorgeeks
17. boolean contains(string) :
Returns true if string contains contains the given string
String s1="geeksforgeeks";
String s2="geeks";
s1.contains(s2) // return true
18. Char[] toCharArray():
Converts this String to a new character array.
String s1="geeksforgeeks";
char []ch=s1.toCharArray(); // returns [ 'g', 'e' , 'e' , 'k' , 's' , 'f', 'o', 'r' , 'g' , 'e' , 'e' , 'k' ,'s' ]
19. boolean starsWith(string):
Return true if string starts with this prefix.
String s1="geeksforgeeks";
String s2="geeks";
s1.startsWith(s2) // return true
Example of String Constructor and String Methods
Below is the implementation of the above mentioned topic:
Java
// Java code to illustrate different constructors and methods// String class.import java.io.*;import java.util.*;// Driver Classclass Test{ // main function public static void main (String[] args) { String s= "GeeksforGeeks"; // or String s= new String ("GeeksforGeeks"); // Returns the number of characters in the String. System.out.println("String length = " + s.length()); // Returns the character at ith index. System.out.println("Character at 3rd position = " + s.charAt(3)); // Return the substring from the ith index character // to end of string System.out.println("Substring " + s.substring(3)); // Returns the substring from i to j-1 index. System.out.println("Substring = " + s.substring(2,5)); // Concatenates string2 to the end of string1. String s1 = "Geeks"; String s2 = "forGeeks"; System.out.println("Concatenated string = " + s1.concat(s2)); // Returns the index within the string // of the first occurrence of the specified string. String s4 = "Learn Share Learn"; System.out.println("Index of Share " + s4.indexOf("Share")); // Returns the index within the string of the // first occurrence of the specified string, // starting at the specified index. System.out.println("Index of a = " + s4.indexOf('a',3)); // Checking equality of Strings 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); //If ASCII difference is zero then the two strings are similar int out1 = s1.compareTo(s2); System.out.println("the difference between ASCII value is="+out1); // Converting cases String word1 = "GeeKyMe"; System.out.println("Changing to lower Case " + word1.toLowerCase()); // Converting cases String word2 = "GeekyME"; System.out.println("Changing to UPPER Case " + word2.toUpperCase()); // Trimming the word String word4 = " Learn Share Learn "; System.out.println("Trim the word " + word4.trim()); // Replacing characters 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 and our helpfull users.
