Java - convert String to int
The best way to convert String to int in java:
xxxxxxxxxxString text = "123";int number = Integer.parseInt(text);System.out.println(number); // 123Other short solutions:
xxxxxxxxxx// solution 2Integer number = Integer.valueOf("123"); // 123// solution 3Integer number = new Integer("123"); // 123// solution 4Integer number = Integer.decode("123"); // 123// solution 5 - with GuavaInteger number = Ints.tryParse("123"); // 123In this post we will cover couple of different ways how to convert String to int or Integer.
Convert String "123" to primitive int with Integer.parseInt()
xxxxxxxxxxpublic class Example1 { public static void main(String[] args) { String text = "123"; int number = Integer.parseInt(text); System.out.println(number); // 123 }}Output:
xxxxxxxxxx123Convert String "123" to Integer object with Integer.valueOf()
xxxxxxxxxxpublic class Example2 { public static void main(String[] args) { String text = "123"; Integer number = Integer.valueOf(text); System.out.println(number); // 123 }}Output:
xxxxxxxxxx123xxxxxxxxxxpublic class Example3 { public static void main(String[] args) { String text = "123"; Integer number = new Integer(text); System.out.println(number); // 123 }}Output:
xxxxxxxxxx123xxxxxxxxxxpublic class Example4 { public static void main(String[] args) { String text = "123"; Integer number = Integer.decode(text); System.out.println(number); // 123 }}Output:
xxxxxxxxxx123xxxxxxxxxximport com.google.common.primitives.Ints;public class Example5 { public static void main(String[] args) { String text = "123"; Integer number = Ints.tryParse(text); System.out.println(number); // 123 }}Output:
xxxxxxxxxx123Both methods:
Integer.parseInt("123")Integer.valueOf("123")
accepts plus sign '+' and minut sign '-'.
Code example:
xxxxxxxxxxpublic class Example6 { public static void main(String[] args) { // Integer.parseInt() - returns int System.out.println(Integer.parseInt("123")); // 123 System.out.println(Integer.parseInt("+123")); // 123 System.out.println(Integer.parseInt("-123")); // -123 // Integer.valueOf() - returns Integer System.out.println(Integer.valueOf("123")); // 123 System.out.println(Integer.valueOf("+123")); // 123 System.out.println(Integer.valueOf("-123")); // -123 }}Output:
xxxxxxxxxx123123-123123123-123xxxxxxxxxxpublic class Example7 { public static void main(String[] args) { String text = "123a"; int number = Integer.parseInt(text); System.out.println(number); }}Output:
xxxxxxxxxxException in thread "main" java.lang.NumberFormatException: For input string: "123a" at java.lang.NumberFormatException.forInputString(NumberFormatException.java:65) at java.lang.Integer.parseInt(Integer.java:580) at java.lang.Integer.parseInt(Integer.java:615)Both methods:
Integer.parseInt("123")Integer.valueOf("123")
will throw java.lang.NumberFormatException if we try to parse anything else then:
digits or '+', '-' as first character.
As stated in java docs of Integer.parseInt()
The characters in the string must all be decimal digits, except that the first character may be an ASCII minus sign '-' ('\u002D') to indicate a negative value or an ASCII plus sign '+' ('\u002B') to indicate a positive value.
Throws:
NumberFormatException - if the string does not contain a parsable integer
We can convert string to integer by implementing our own atoi() method. ATOI stands for ASCII to integer. Take a look at this atoi java implementation:
ASCII to int - Java implementation
