Java.lang.String class in Java | Set 2

Difficulty Level : Easy
Last Updated : 23 Jul, 2020

Java.lang.String class in Java | Set 1
In this article we would be discussing different constructor and methods provided by java.lang.String. Strings in java are immutable.
Now lets discuss some of the methods provided by String class.
Methods:

public int codePointAt(int index) – It takes as parameter a index which must be from 0 to length() – 1. ad returns a character unicode point of a index.
public int codePointBefore(int index) – It takes as parameter a index which must be from 0 to length() – 1. and returns a unicode point of a character just before the index .

public int codePointCount(int start_index, int end_index) – It takes as parameter start_index and end_index and returns the count of Unicode code points between the range.

Lets see an example of the above methods:
Example:

// Java Program to demonstrate codePointAt
// codePointBefore and codePointCount
public class GFG_1 {
public static void main(String[] args)
    {
  
        String s = "GeeksforGeeks";
  
        // codePointAt()
        System.out.print("Character (unicode point) at index 1 : "
                         + s.codePointAt(1) + "  ");
        System.out.println(s.codePointAt(5));
  
        // codePointBefore()
        System.out.print("Character (unicode point) before index 1 : "
                         + s.codePointBefore(1) + "  ");
        System.out.println(s.codePointBefore(7));
  
        // codePointCount()
        s = "G eek123 G**k";
        System.out.println("Character code point count : "
                           + s.codePointCount(0, 5));
    }
}

Output:

Character (unicode point) at index 1 : 101  102
Character (unicode point) before index 1 : 71  111
Character code point count : 5

public CharSequence subSequence(int start_index, int end_index) – This method returns CharSequence which is a subsequence of the String on which this method is invoked.
Note: It behaves similarly to subString(int start_index, int end_index), but subString() returns String while subSequence returns CharSequence.
public boolean contains(CharSequence char_seq) – It returns true if the given CharSquence is present in the String on which its invoked.

public boolean contentEquals(CharSequence char_seq) – It returns true only if the given CharSequence exactly matches the String on which its invoked

Lets see an example of the above methods:
Example:

// Java Program to demonstrate subSequence
// and contains and contentEquals
public class GFG_2 {
public static void main(String[] args)
    {
        String s = "geeksforgeeks";
  
        // subSequence()
        // contains "for"
        CharSequence cs = s.subSequence(5, 8);
  
        // contains "geeks"
        CharSequence cs1 = s.subSequence(0, 5);
  
        String s_1 = "geekforgeek";
  
        // contains()
        System.out.println("Reult of contains on s_1 "
                           + "with charSequence cs " + s_1.contains(cs));
        System.out.println("Reult of contains on s_1 "
                           + "with charSequence cs1 " + s_1.contains(cs1));
  
        // contentEqual()
  
        System.out.print("Result of contentEqual ");
        System.out.println("geeks".contentEquals(cs1));
  
        System.out.print("Result of contentEqual ");
        System.out.println("geeksfor".contentEquals(cs1));
    }
}

Output:

Reult of contains on s_1 with charSequence cs true
Reult of contains on s_1 with charSequence cs1 false
Result of contentEqual true
Result of contentEqual false

public boolean endsWith(String suf) – It takes in parameter a String suffix and return true if the String has same suffix.

public boolean startsWith(String pre) – It takes in parameter a String prefix and returns true if the String has a same prefix

Lets see an example of the above methods:
Example:

// Java Program to demonstrate endsWith
// and startWith
public class GFG_3 {
public static void main(String[] args)
    {
  
        String s = "geeksforgeeks";
  
        // endsWith
        String ends_1 = "geeks";
        String ends_2 = "eks";
        String ends_3 = "for";
  
        System.out.println(s + "end with " + ends_1 + " " + s.endsWith(ends_1));
        System.out.println(s + "end with " + ends_2 + " " + s.endsWith(ends_2));
        System.out.println(s + "end with " + ends_3 + " " + s.endsWith(ends_3));
  
        // startWith
        String start_1 = "geeks";
        String start_2 = "for";
  
        System.out.println(s + " starts with " + start_1
                           + "  " + s.startsWith(start_1));
        System.out.println(s + " starts with " + start_2
                           + "  " + s.startsWith(start_2));
    }
}

Output:

geeksforgeeksend with geeks true
geeksforgeeksend with eks true
geeksforgeeksend with for false
geeksforgeeks starts with geeks  true
geeksforgeeks starts with for  false

public void getChars(int start, int end, char[] destination, int destination_start) : It takes in four parameters, start and end refers to the range which is to copied to the character array, destination is the character array to be copied to, and destination_start is the starting location of the destination array.

public char[] toCharArray() – It coverts the entire String to the character array.

Note :- getChars provide more flexibility when, a range of characters is to be copied to an exiting array or a new array while toCharArray converts the entire string to a new character array.

Lets see an example of the above methods:
Example:

// Java Program to demonstrate getChars
// and toCharArray
public class GFG_4 {
public static void main(String args[])
    {
        String s = "geeksforgeeks";
  
        // toCharArray
        char[] arr;
        arr = s.toCharArray();
        System.out.println("String toCharArray: ");
        for (char i : arr)
            System.out.print(i + " ");
  
        // getChars
        s.getChars(5, 8, arr, 0);
        System.out.println("\nSubString to existing "
                           + "char array");
        for (char i : arr)
            System.out.print(i + " ");
    }
}

Output:

String toCharArray: 
g e e k s f o r g e e k s 
SubString to existing char array
f o r k s f o r g e e k s

public int hashCode() – It returns hashcode of the given String. There is predefined formula to compute the hashcode of the String:
```
s[0]*31^(n-1) + s[1]*31^(n-2) + ... + s[n-1]
where,
n - is the length of the String
i - is the ith character of the string
```

public String intern() – It returns the canonical form of the String object on which it is invoked.
” When the intern method is invoked, if the pool already contains a string equal to this String object as determined by the equals(Object) method, then the string from the pool is returned. Otherwise, this String object is added to the pool and a reference to this String object is returned. ” – Java String Documentation.

Lets see an example of the above method:-
To understand the example better refer to Initialize and compare String
Example:

// Java program to demonstrate
// hashCode and intern
class GFG_5 {
public static void main(String[] args)
    {
  
        // hashCode
        String s = "geeks";
        System.out.println("Hashcode of String s is "
                           + s.hashCode());
  
        // intern()
        String s_1 = "geeks";
        String s_2 = new String("geeks");
        String s_3 = s_2.intern();
  
        // returns true
        System.out.println(s_1 == s_2);
  
        // returns false
        System.out.println(s_1 == s_3);
    }
}

Output:

Hashcode of String s is 98232047
false
true

public boolean isEmpty() – It returns true if the length of the String is 0.

public static String format(String f, Object… arguments) – Returns the formatted String according to the format specifier f, the arguments should exactly equal to the number of format specifier used .
Variation:
public static String format(Locale l, String f, Object… arguments)– Returns the formatted String as per Locale used.

Lets see an example of the above methods:
Example:

import java.util.Locale;
// Java program to demonstrate
// isEmpty and format
class GFG_6 {
public static void main(String[] args)
    {
  
        String s = "geeksforgeeks";
  
        // format()
        String s1 = String.format("%s : %d", s, 10);
        System.out.println(s1);
  
        String s2 = String.format("%s = %f ",
                                  "Value of PI is", Math.PI);
        System.out.println(s2);
  
        // format() with locale
        // we are using the default locale here
  
        String s3 = String.format(Locale.getDefault(),
                                  "%s : %d", s, 10);
        System.out.println(s3);
  
        // isEmpty
        String s4 = "";
        System.out.println("is String s empty "
                           + s.isEmpty());
  
        System.out.println("is String s4 empty? "
                           + s4.isEmpty());
    }
}

Output:

geeksforgeeks : 10
Value of PI is = 3.141593 
geeksforgeeks : 10
is String s empty false
is String s4 empty? true

public boolean matches(String reg_exp) – It returns true if the string matches the regular expression( reg_exp).

public boolean regionMatches(int start_OString, String another, int start_AString, int no_of_char) – It returns true if the region of original string staring with index start_OString matches with the region of another string starting with string_AString, and no_of_char refers to the number of character to be compared.

Variation :
public boolean regionMatches(boolean ignore_case, int start_OString, String another, int start_AString, int no_of_char) – This variation of a method provide flexibility when we want to ignore the case while comparing substring. If the first parameter i.e. ignore_case is true it neglects the case and compares but if it is false it behaves similarly as the first version of the method without ignore_case

Lets see an example of the above methods:
Example:

// Java Program to demonstrate
// matches and regionMatches
class GFG_7 {
public static void main(String[] args)
    {
        String s = "geeksforGeeks";
  
        // matches
        System.out.println("Matches 1 :"
                           + s.matches("(.*)Geeks"));
        System.out.println("Matches 2 :"
                           + s.matches("(.*)for(.*)"));
        System.out.println("Matches 3 :"
                           + s.matches("geeksfor"));
  
        // regionMatches(int, String, int, int)
  
        String s2 = "Geeksforgeeks";
  
        System.out.println("RegionMatches 1 :" + s.regionMatches(5, s2, 5, 3));
        System.out.println("RegionMatches 2 :" + s.regionMatches(5, s2, 6, 3));
  
        // regionMatches(boolean, int, String, int, int)
        // ignore the case while comparing
        System.out.println("Region Matches 3 :" + s.regionMatches(true, 0, s2, 0, 3));
  
        // consider the case while comparing
        System.out.println("Region Matches 3 :" + s.regionMatches(false, 0, s2, 0, 3));
    }
}

Output:

Matches 1 :true
Matches 2 :true
Matches 3 :false
RegionMatches 1 :true
RegionMatches 2 :false
Region Matches 3 :true
Region Matches 3 :false

public String[] split(String reg_exp) – It splits the string around the regular expression and returns a String array.

Variation :
public String[] split(String reg_exp, int limit) – It splits the string around the regular expression and limit refers to the number of times the reg_exp is applied and it is the length of the resulting array and reg_exp is n is applied only length – 1 times.

Lets see an example of the above methods:
Example:

// Java Program to demonstrate
// split
class GFG_8 {
public static void main(String[] args)
    {
        String s = "Geeks for Geeks";
  
        // split
        System.out.println("Splitting the string a"
                           + "round spaces");
        String[] geek_arr = s.split("\\s+");
        for (String i : geek_arr)
            System.out.println(i);
  
        System.out.println("\nSplitting the string around the spaces"
                           + "\nbut controlling the length of resulting array :");
        String s_1 = "Geeks for Geeks Geeks for Geeks";
        String[] geek_arr1 = s_1.split("\\s+", 2);
        for (String i : geek_arr1)
            System.out.println(i);
  
        System.out.println("\nSplitting the string around the spaces"
                           + "\nbut controlling the length of resulting array :");
        geek_arr1 = s_1.split("\\s+", 4);
        for (String i : geek_arr1)
            System.out.println(i);
    }
}

Output:

Splitting the string around spaces
Geeks
for
Geeks

Splitting the string around the spaces
but controlling the length of resulting array :
Geeks
for Geeks Geeks for Geeks

Splitting the string around the spaces
but controlling the length of resulting array :
Geeks
for
Geeks
Geeks for Geeks

public static String join(CharSequence de_limiter, CharSequence… elements) – It returns a string which contains all the elements joins by the de_limiter.

Variation:
public static String join(CharSequence de_limiter, Iterable elements) – It performs the same function but the second parameter is Iterable which makes it flexible to work with different collection classes.

Lets see an example of the above methods:
Example:

// Java Program to demonstrate
// join
import java.util.LinkedList;
class GFG_9 {
public static void main(String[] args)
    {
        // join()
        System.out.print("Example of join 1 : ");
        System.out.println(
            String.join(", ", "Geeks", "for", "Geeks"));
  
        System.out.print("Example of join 2 : ");
        LinkedList ll = new LinkedList();
        ll.add("browsing");
        ll.add("geeks");
        ll.add("for");
        ll.add("geeks");
        ll.add("is");
        ll.add("fun");
        System.out.println(String.join("-a-", ll));
    }
}

Output:

Example of join 1 : Geeks, for, Geeks
Example of join 2 : browsing-a-geeks-a-for-a-geeks-a-is-a-fun

public String replaceAll(String reg_exp, String replacement) – It replaces all the Substring of the original string that matches the reg_exp with replacement and returns the modified String.

public String replaceFirst(String reg_exp, String replacement) – It replaces the first occurrence of the reg-exp in the original string with the replacement and returns the modified String.
Note :- replaceAll and replaceFirst does’nt changes the original String rather it creates a new string with modification.

Lets see an example of the above methods:
Example:

// Java Program to demonstrate
// replaceAll and replaceFirst
class GFG_10 {
public static void main(String[] args)
    {
        String s = "GeeksforGeeks";
        ;
  
        // replaceAll()
        String s1 = s.replaceAll("Geeks", "Quiks");
        System.out.println("Replace all Geeks "
                           + "with Quiks :" + s1);
  
        System.out.print("Replace any UpperCase letter "
                         + "with F :");
        System.out.println(s.replaceAll("[A-Z]+", "F"));
  
        // replaceFirst()
        String s2 = s.replaceFirst("Geeks", "Quiks");
        System.out.println("Replace first Occurrence "
                           + "of Geeks with Quiks :" + s2);
    }
}

Output:

Replace all Geeks with Quiks :QuiksforQuiks
Replace any UpperCase letter with F :FeeksforFeeks
Replace first Occurrence of Geeks with Quiks :QuiksforGeeks

For more methods on String refer to String class in java
Reference:
https://docs.oracle.com/javase/8/docs/api/java/lang/String.html

This article is contributed by Sumit Ghosh. If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above.

Attention reader! Don’t stop learning now. Get hold of all the important Java Foundation and Collections concepts with the Fundamentals of Java and Java Collections Course at a student-friendly price and become industry ready. To complete your preparation from learning a language to DS Algo and many more, please refer Complete Interview Preparation Course.

My Personal Notes

Related Articles