StringBuilder Class in Java
In Java, StringBuilder class belongs to java.lang package. It is used to create mutable (modifiable) String. It is same as StringBuffer class except that it is non-synchronized. It is available since JDK 1.5.
We should use StringBuffer class only when thread safety is compulsory; otherwise, prefer StringBuilder for improved performance.
Hierarchy of StringBuilder Class
StringBuilder Class Constructors
| Constructor | Description |
|---|---|
| StringBuilder() | It creates an empty String Builder with the initial capacity of 16. |
| StringBuilder(String str) | It creates a String Builder with the specified string. |
| StringBuilder(int length) | It creates an empty StringBuilder with the specified capacity as length. |
StringBuilder Class Methods
| Method | Description |
|---|---|
| public StringBuilder append(String s) | It is used to append the specified string with this string. The append() method is overloaded like append(char), append(boolean), append(int), append(float), append(double) etc. |
| public StringBuilder insert(int offset, String s) | It is used to insert the specified string with this string at the specified position. The insert() method is overloaded like insert(int, char), insert(int, boolean), insert(int, int), insert(int, float), insert(int, double) etc. |
| public StringBuilder replace(int startIndex, int endIndex, String str) | It is used to replace the string from specified startIndex and endIndex. |
| public StringBuilder delete(int startIndex, int endIndex) | It is used to delete the string from specified startIndex and endIndex. |
| public StringBuilder reverse() | It is used to reverse the string. |
| public int capacity() | It is used to return the current capacity. |
| public void ensureCapacity(int minimumCapacity) | It is used to ensure the capacity at least equal to the given minimum. |
| public char charAt(int index) | It is used to return the character at the specified position. |
| public int length() | It is used to return the length of the string i.e. total number of characters. |
| public String substring(int beginIndex) | It is used to return the substring from the specified beginIndex. |
| public String substring(int beginIndex, int endIndex) | It is used to return the substring from the specified beginIndex and endIndex. |
Java StringBuilder Examples
Let's see the examples of different methods of StringBuilder class.
1) Example: StringBuilder.append() Method
The append() method concatenates the given argument with this String.
Java
public class Main {
public static void main(String args[]){
StringBuilder sb=new StringBuilder("Hello ");
sb.append("Java");//now original string is changed
System.out.println(sb);//prints Hello Java
}
}
Output:
Hello Java
2) StringBuilder.insert() Method
The insert() method inserts the given string with this string at the given position.
Java
public class Main {
public static void main(String args[]){
StringBuilder sb=new StringBuilder("Hello ");
sb.insert(1,"Java");//now original string is changed
System.out.println(sb);//prints HJavaello
}
}
Output:
HJavaello
3) StringBuilder.replace() Method
The replace() method replaces the given string from the specified beginIndex and endIndex.
Java
public class Main {
public static void main(String args[]){
StringBuilder sb=new StringBuilder("Hello");
sb.replace(1,3,"Java");
System.out.println(sb);//prints HJavalo
}
}
Output:
HJavalo
4) StringBuilder.delete() Method
The delete() method deletes the string from the specified beginIndex to endIndex.
Java
public class Main {
public static void main(String args[]){
StringBuilder sb=new StringBuilder("Hello");
sb.delete(1,3);
System.out.println(sb);//prints Hlo
}
}
Output:
Hlo
5) StringBuilder.reverse() Method
The reverse() method reverses the current string.
Java
public class Main {
public static void main(String args[]){
StringBuilder sb=new StringBuilder("Hello");
sb.reverse();
System.out.println(sb);//prints olleH
}
}
Output:
olleH
6) StringBuilder.capacity() Method
The capacity() method returns the current capacity of the Builder. The default capacity of the Builder is 16. If the number of character increases from its current capacity, it increases the capacity by (oldcapacity*2) + 2. For example, if your current capacity is 16, it will be (16*2)+2=34.
Java
public class Main {
public static void main(String args[]){
StringBuilder sb=new StringBuilder();
System.out.println(sb.capacity());//default 16
sb.append("Hello");
System.out.println(sb.capacity());//now 16
sb.append("Java is my favourite language");
System.out.println(sb.capacity());//now (16*2)+2=34 i.e (oldcapacity*2)+2
}
}
Output:
16 16 34
7) StringBuilder.ensureCapacity() Method
The ensureCapacity() method ensures that the given capacity is the minimum to the current capacity. If it is greater than the current capacity, it increases the capacity by (oldcapacity*2)+2. For example, if your current capacity is 16, it will be (16*2)+2=34.
Java
public class Main {
public static void main(String args[]){
StringBuilder sb=new StringBuilder();
System.out.println(sb.capacity());//default 16
sb.append("Hello");
System.out.println(sb.capacity());//now 16
sb.append("Java is my favourite language");
System.out.println(sb.capacity());//now (16*2)+2=34 i.e (oldcapacity*2)+2
sb.ensureCapacity(10);//now no change
System.out.println(sb.capacity());//now 34
sb.ensureCapacity(50);//now (34*2)+2
System.out.println(sb.capacity());//now 70
}
}
Output:
16 16 34 34 70
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