String Methods in Java

In Java, instance methods are methods called using an object.
Example:

String s = "Java";
System.out.println(s.length());

Here length() is an instance method.

Common properties
Access modifier → public
Constructor → No (these are methods)
Final → Most methods are not declared final
Called using object

Example:

String s = "Java";
s.length();

1. length()
Returns number of characters.

String s = "Java";
System.out.println(s.length());

Output:
4

2. charAt(int index)
Returns character at index.

String s = "Java";
System.out.println(s.charAt(2));

Output:
v

3. substring()
Extracts part of string.

String s = "Java";
System.out.println(s.substring(1,3));

Output:
av

4. equals()
Compares content.

String a = "java";
String b = "java";
System.out.println(a.equals(b));

Output:
true

5. equalsIgnoreCase()
Ignores uppercase/lowercase.

String a = "JAVA";
System.out.println(a.equalsIgnoreCase("java"));

Output:
true

6. compareTo()
Compares alphabetically.

System.out.println("apple".compareTo("banana"));

Output:
negative value

7. contains()
Checks if string exists.

String s = "Java Programming";
System.out.println(s.contains("Java"));

Output:
true

8. concat()
Joins strings.

String s = "Java";
System.out.println(s.concat(" SQL"));

Output:
Java SQL

9. toUpperCase()
Converts to uppercase.

String s = "java";
System.out.println(s.toUpperCase());

Output:
JAVA

10. toLowerCase()
Converts to lowercase.

String s = "JAVA";
System.out.println(s.toLowerCase());

Output:
java

11. trim()
Removes spaces at beginning/end.

String s = "  Java  ";
System.out.println(s.trim());

Output:
Java

12. startsWith()
Checks starting characters.

String s = "Java";
System.out.println(s.startsWith("Ja"));

Output:
true

13. endsWith()
Checks ending characters.

String s = "Java";
System.out.println(s.endsWith("va"));

Output:
true

14. indexOf()
Returns first index.

String s = "Java";
System.out.println(s.indexOf("a"));

Output:
1

15. replace()
Replaces characters.

String s = "Java";
System.out.println(s.replace('a','o'));

Output:
Jovo

16. split()
Splits string into array.

String s = "A-B-C";
String[] arr = s.split("-");

Output array:
A
B
C

Constructor of String
Constructors create String objects.

Example:
String s = new String("Java");

Some constructors:
Constructor
public String()
public String(String original)
public String(char[] value)
public String(byte[] bytes)
Simple summary

String instance methods:
are mostly public
called using object
return different types
help in:
searching
comparing
extracting
converting
modifying strings (by creating new strings)