String and StringBuffer
String and StringBuffer
In Java, String and StringBuffer are both used to work with text, but the major difference is that String is immutable, while StringBuffer is mutable.
String
A String object cannot be changed after it is created. Any operation that appears to modify a string actually creates a new String object.
String s = "Hello"; s = s + " World"; System.out.println(s);
Here, "Hello" is not modified. A new String "Hello World" is created.
Common String Methods
| Method | Purpose | Example | |
|---|---|---|---|
| length() | Returns number of characters | s.length() | |
| charAt() | Returns character at index | s.charAt(0) | |
| concat() | Joins strings | s.concat(" World") | |
| equals() | Compares contents | s.equals("Hello") | |
| equalsIgnoreCase() | Compares ignoring case | s.equalsIgnoreCase("hello") | |
| substring() | Extracts part of string | s.substring(1, 4) | |
| toUpperCase() | Converts to uppercase | s.toUpperCase() | |
| toLowerCase() | Converts to lowercase | s.toLowerCase() | |
| indexOf() | Finds position | s.indexOf("l") | |
| replace() | Replaces characters/text | s.replace('l', 'x') | |
| trim() | Removes leading/trailing spaces | s.trim() | |
| contains() | Checks whether text exists | s.contains("ell") |
Example
String s = "Hello";
System.out.println(s.length()); // 5
System.out.println(s.charAt(1)); // e
System.out.println(s.toUpperCase()); // HELLO
System.out.println(s.substring(1, 4)); // ell
System.out.println(s.indexOf('l')); // 2
System.out.println(s.replace('l', 'x')); // Hexxo
String Buffer
StringBuffer represents a modifiable sequence of characters.
StringBuffer sb = new StringBuffer("Hello");
sb.append(" World");
System.out.println(sb);
Important StringBuffer methods
| Method | Purpose | Example |
|---|---|---|
| append() | Adds text at the end | sb.append(" Java") |
| insert() | Inserts text at a position | sb.insert(5, " Java") |
| delete() | Deletes characters | sb.delete(5, 10) |
| deleteCharAt() | Deletes one character | sb.deleteCharAt(2) |
| replace() | Replaces part of text | sb.replace(0, 5, "Hi") |
| reverse() | Reverses the sequence | sb.reverse() |
| charAt() | Gets character | sb.charAt(0) |
| setCharAt() | Changes a character | sb.setCharAt(0, 'J') |
| length() | Returns length | sb.length() |
| capacity() | Returns current capacity | sb.capacity() |
| substring() | Returns part as String | sb.substring(1, 4) |
| toString() | Converts to String | sb.toString() |
StringBuffer sb = new StringBuffer("Hello");
sb.append(" Java");
System.out.println(sb); // Hello Java
sb.insert(5, " World");
System.out.println(sb); // Hello World Java
sb.delete(5, 11);
System.out.println(sb); // Hello Java
sb.setCharAt(0, 'Y');
System.out.println(sb); // Yello Java
sb.reverse();
System.out.println(sb); // avaJ olleY