Top 13 String Functions in Java | Java String [With Examples]

String functions are the backbone of any coding language, and the versatile nature of these functions provided by Java is the best. So let us discuss the common string functions and their applications.

How to read a line from the console:  use nextLine method

Scanner in = new Scanner(System.in);

String line = in.nextLine();

1. Indexing

We can access the character of a string using charAt(int pos) method.

ex:

String h = “hello world”;

System.out.println(h.charAt(4));

2. Getting a Position

This is the most frequent operation performed during string manipulation.

1. If you need position of any symbol, use indexOf(). It returns a numeric value (position) of a symbol.

ex: 

String para=”Batman is protector of gotham”;

int pos1 = para.indexOf(‘a’); //  1

int pos2 = para.indexOf(‘z’) // -1

2. The java string lastIndexOf() method returns the last index of the given character value or substring. If it is not found, it returns -1. The index counter starts from zero.

ex:

String para=”Batman is protector of gotham”;

int pos = para.lastIndexOf(‘a’); // 27

int pos2 = para.indexOf(‘z’) // -1

3. Pattern Matching

The java string contains() method searches the sequence of characters in the string. It returns true if a sequence of char values are found in this string otherwise returns false.

ex:

String name=”Batman is protector of gotham”;  

System.out.println(name.contains(“man is”));  // true

System.out.println(name.contains(“of gotham”));  // true

System.out.println(name.contains(“protector of metropolis”)); // false

4. Checking Prefix and Suffixes

1. startsWith()  :

String s=”Optimus Prime”;

System.out.println(s.startsWith(“Op”));//true

2. endsWith() :

String s=”Optimus Prime”;

System.out.println(s.endsWith(“me”));//true

5. Converting Other Data Types to String

This can be done by Java String valueOf() method. It converts given types such as int, long, float, double, boolean, char and char array into string.

ex:

int number=100;  // similarly we can convert another data types too

String str=String.valueOf(number);

System.out.println(str+10);

6. If Length of a String is Needed

Use the length() method of the string. It returns a count of the total number of characters.

ex:

String h = “hello world”;

int size = h.length()

7. To Check Whether a String is Empty

The java string isEmpty() method checks if this string is empty or not. It returns true, if the length of string is 0 otherwise false.

ex:

String s1=””;

String s2=”coding is divine”;

System.out.println(s1.isEmpty());  // print true

System.out.println(s2.isEmpty());  // print false

8. Getting Substring

If you need a subpart of String then java provides an elegant way of doing this by the following methods.

1. substring(int beginIndex): This method returns a new string that is a substring of this string. The substring begins with the character at the specified index and extends to the end of this string.

ex:

String str = “Hello World”;

String firstPart = str.substring(4);

2. substring(int beginIndex, int endIndex): The substring begins at the specified beginIndex and extends to the character at index endIndex – 1. Thus the length of the substring is (endIndex – beginIndex).

ex:

String str = “Hello World”;

String new_string = str.substring(1,6); // remember [ firstindex,lastindex )

9. If Want to Compare Two Different Strings

1. equals() method: It compares the two given strings based on the content of the string. If any character is not matched, it returns false. If all characters are matched, it returns true.

ex:

String s1=”Freelancer”;

String s2=”Freelancer”;

String s3=”freelancer”;

String s4=”java”;

System.out.println(s1.equals(s2));//true because content and case is same

System.out.println(s1.equals(s3));//false because case is not same

System.out.println(s1.equals(s4));//false because content is not same

2. String.equalsIgnoreCase(): The String.equalsIgnoreCase() method compares two strings irrespective of the case (lower or upper) of the string. This method returns true if the argument is not null and the contents of both the Strings are the same ignoring case, else false.

ex:

String s1=”Freelancer”;  

String s2=”Freelancer”;  

String s3=”freeLancer”;  

String s4=”java”;  

System.out.println(s1.equalsIgnoreCase(s2));//true because content and case is same  

System.out.println(s1.equalsIgnoreCase(s3));//true because content same but cases are not same  

System.out.println(s1.equalsIgnoreCase(s4));//false because content is not same

10. If We Want to Join Two Different Strings

Java provides the best method to join different strings by using concat method.

ex:

String s1=”love is immortal”;

String s2=” and coding is divine “;

String joined_string = s1.concat(s2);

System.out.println(joined_string); // prints love is immortal and coding is divine

11. If We Want to Change and Modify a String by Using Another String

We can use the replace() method using two ways.

1. replacing characters of string by another string’s character

ex:

String s1=”Every human can be extraordinary”;

String replacedString=s1.replace(‘a’,’e’);//replaces all occurrences of ‘a’ to ‘e’

System.out.println(replacedString);

2. replace words of a string with words of another string

ex:

String s1=” java can be replaced by python and it can lose its charm”;

String replaceString=s1.replace(“can”,”cannot”);//replaces all occurrences of “can” to “cannot”

System.out.println(replaceString);

12. Changing Cases of a String

1. string toLowerCase(): method returns the string in the lowercase letter. In other words, it converts all characters of the string into lower case letters.

ex:

String temp=”This is Uppercase And Lower Case String “;

String temp_lower=temp..toLowerCase();

System.out.println(temp_lower); //  “this is uppercase and lower case string “

2. Java string toUpperCase()  : method returns the string in uppercase letter. In other words, it converts all characters of the string into upper case letters.

ex:

String temp=”This is Uppercase And Lower Case String “;

String temp_upper=temp.toUpperCase();

System.out.println(temp_upper);   // “THIS IS UPPERCASE AND LOWER CASE STRING”

13. Eliminates Leading and Trailing Spaces

The java string trim() method eliminates leading and trailing spaces. Note: The string trim() method doesn’t omit middle spaces.

ex:

String s1=”  hello string   “;

System.out.println(s1+”coder”);//without trim()

String trimmed_string = s1.trim();

System.out.println(trimmed_string+”coder”);//with trim()

Conclusion

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