2 Ways To Parse String To Int Inward Java

Java provides Integer.parseInt() method to parse a String to an int value, merely that's non the exclusively means to convert a numeric String to int inward Java. There is, inward fact, a amend way, which takes wages of the parsing logic of parseInt() method every bit good every bit caching offered past times Flyweight blueprint pattern, which makes it to a greater extent than efficient together with useful. Yes, you lot guessed it right, I am talking almost Integer.valueOf() method, which implements Flyweight blueprint pattern together with maintains a cached puddle of ofttimes used int values e.g. from -128 to 127. So every fourth dimension you lot overstep a numeric String which is inward the hit of -128 to 127, Integer.valueOf() doesn't create a novel Integer object merely render the same value from cached pool. The exclusively drawback is that Integer.valueOf() returns an Integer object together with non an int primitive value similar parseInt() method, merely given auto-boxing is available inward Java from JDK five onward, which automatically convert an Integer object to int value inward Java.

2 Examples to Parse String to int inward Java

Here is our Java programme to convert String to int inward Java. This instance shows how to purpose both Integer.parseInt() together with Integer.valueOf() method to parse a numeric String to an int primitive inward Java. In this program, nosotros inquire the user to travel into a number together with thus nosotros read user input from the console using Scanner cast every bit String. Later nosotros convert that String using both Integer.parseInt() together with Integer.valueOf() method to demo that both methods run together with you lot tin dismiss purpose either of them.




Java Program to Parse String to Int

import java.util.Scanner;  /**  * two ways to convert String to int inward Java.  * User enters number, nosotros read it every bit String together with convert it to int using parseInt() method.  *   * @author WINDOWS 8  *  */ public class StringToInt {      public static void main(String args[]) {         System.out.println("Please travel into an integer number");                Scanner scnr = new Scanner(System.in);        String input = scnr.nextLine();                int i = Integer.parseInt(input);                System.out.println("String converted to int : " + i);                System.out.println("Please travel into closed to other integer number");                String str = scnr.nextLine();                int j = Integer.valueOf(str); // tin dismiss render cached value                System.out.println("String to int using valueOf() : " + j);              }       }  Output : Please travel into an integer number 100 String converted to int : 100 Please travel into closed to other integer number 300 String to int using valueOf() : 300

You tin dismiss come across that both Integer.valueOf() together with Integer.parseInt() method is able to parse a numeric String. You tin dismiss fifty-fifty overstep a numeric String amongst Plus together with Minus sign, both methods are capable of parsing them successfully every bit shown below :

Please travel into an integer number +201 String converted to int : 201 Please travel into closed to other integer number -203 String to int using valueOf() : -203

merely if you lot overstep a String which contains anything other than +, - together with digits, you lot volition acquire java.lang.NumberFormatException every bit shown below :

Please travel into an integer number ++201 Exception in thread "main" java.lang.NumberFormatException: For input string: "++201"     at java.lang.NumberFormatException.forInputString(Unknown Source)     at java.lang.Integer.parseInt(Unknown Source)     at java.lang.Integer.parseInt(Unknown Source)     at dto.ReverseIntegerTest.main(ReverseIntegerTest.java:22)

You tin dismiss come across fifty-fifty double sign is besides non allowed, let's endeavor an alphanumeric String :

Please travel into an integer number 2012a44 Exception in thread "main" java.lang.NumberFormatException: For input string: "2012a44"     at java.lang.NumberFormatException.forInputString(Unknown Source)     at java.lang.Integer.parseInt(Unknown Source)     at java.lang.Integer.parseInt(Unknown Source)     at dto.ReverseIntegerTest.main(ReverseIntegerTest.java:22)

You tin dismiss come across that Integer.parseInt() doesn't similar anything other valid values inward numeric String. You volition acquire same errors fifty-fifty if you lot purpose Integer.valueOf() method because valueOf() method internally calls parseInt() method to parse String to integer inward Java.

That's all almost how to parse String to int inward Java. Even though parseInt() is the criterion means to parse String to int, you lot should endeavor to purpose Integer.valueOf() method. It implements Flyweight blueprint pattern together with maintains a puddle of ofttimes used int values e.g. int primitives from -128 to 127 together with that's how it relieve retention together with time.

Though, you lot bespeak to last careful piece comparison it because if you lot purpose  equality operator (== )then Java compare their references together with render truthful exclusively if both variables are pointing to the same object e.g. ane of the Integer objects returned from a cached pool.

So you lot mean value that == operator is working merely thus you lot volition come across issues when Integer object is exterior of that range, inward that case, == operator volition non work. In short, you lot receive got created a põrnikas which is difficult to find. See this story to larn to a greater extent than almost this bug.

 BTW, if you lot are learning Java together with desire to master copy fundamentals, I advise you lot receive got a await at Head First Java 2d Edition, they explicate the concept inward the easiest means possible merely besides brings out of import details.

If you lot are novel to Java together with wants to larn almost how to convert ane type to another, cheque out my next information type conversion tutorials :

• How to convert String to Double inward Java? (example)
• How to convert ByteBuffer to String inward Java? (program)
• How to convert double to Long inward Java? (program)
• How to convert float to String inward Java? (example)
• How to convert byte array to String inward Java? (program)
• How to convert Enum to String inward Java? (example)
• How to convert String to int inward Java? (example)
• How to convert Decimal to Binary inward Java? (example)
• How to convert String to Date inward a thread-safe manner? (example)
• How to parse String to long inward Java? (answer)

Further Learning
Data Structures together with Algorithms: Deep Dive Using Java
Java Fundamentals: The Java Language
Complete Java Masterclass