String to Integer in Java – Convert String to Int – Scaler Topics

Overview

Integer.parseInt() and Integer.valueOf() methods can be used to convert String to int in Java. These methods are defined under the Integer class in java.lang package. Both methods throw NumberFormatException when the String input contains characters other than digits.

Scope

This article aims to:

• Explain how to use

  Integer.parseInt()

  and

  Integer.valueOf()

  methods.

• Illustrate the

  NumberFormatException

  thrown by these methods.

Introduction

You are in your computer lab trying to formulate a complex Java equation that will surely be a boon to mankind. Variables are racing in your head, and equations are wandering. You are very close to the solution and require a multiplication to a string.

All you want to do is convert a string to int, multiply the value and submit your equation. The thought of being stuck at the endpoint made you search the web, and you came across this article to convert String to an int in Java.

This article explains two methods of converting a String to an integer in Java:

1. Integer.parseInt()
2. Integer.valueOf()

Integer.parseInt() method converts String to int (primitive data type) in Java. However, Integer.valueOf() method can be used to convert String to an instance of the Integer class in Java.

Integer.parseInt() – Converts String to int

The parseInt() method converts a String to a primitive (basic) data type, i.e., int in Java. The parseInt() method is a static method of Integer class.

Signature of parseInt() method

public
 
static
 
int
 
parseInt
(String input)



Syntax
int
 val = Integer.parseInt(
"200"
);


Example
String str = 
"5678"
;
int
 value = Integer.parseInt(str);


Let’s see an example of converting String to int in Java.
Code:
class
 
Example
 
{

  
public
 
static
 
void
 
main
(String args[])
 
{
    
// String literal

    String str = 
"123"
;

    
// Holds the integer equivalent

    
int
 ans = Integer.parseInt(str);

     System.out.println(ans);
   }
 }


Output:
123



Integer.parseInt(String s, int radix) – Converts String to int
The Integer.parseInt(String s) method uses the default radix as 10 to parse the string input. It means the string input is interpreted as a decimal number while conversion by default.
Specifying the radix input to Integer.parseInt method would set the static method to use it as base number in parsing the input string argument. For example, if the string value is expected to be in hexadecimal format, we would be invoking the method like this:
Integer.parseInt(
"A1E"
, 
16
); 
// 2590 in base 10



Signature of parseInt(String s, int radix) method
public
 
static
 
int
 
parseInt
(String input, 
int
 radix)



Syntax
int
 val = Integer.parseInt(
"101"
, 
2
); 
// val = 5



Example
String str = 
"1010"
;
int
 value = Integer.parseInt(str, 
2
);


Let’s see an example of converting String (in a specified base) to int in Java.
Code:
class
 
Example
 
{

  
public
 
static
 
void
 
main
(String args[])
 
{
    
// String literal in base 2

    
// 1011 in base 2 implies 11 in base 10

    String str = 
"1011"
;

    
// Holds the integer equivalent i.e. 11

    
int
 ans = Integer.parseInt(str, 
2
);

     System.out.println(ans);
   }
 }


Output:
11


Integer.valueOf() – Converts String to int
Integer.valueOf() method returns the Integer object when a string literal is passed as an argument. It takes in the string or an integer as a first argument and converts it into an Integer object. This works the same as parseInt() and changes a string to an integer in java for the radix argument.
Syntax:
Integer.valueOf(String s)
Integer.valueOf(String s, 
int
 radix) 
// radix = base of String s



Example:
String str = 
"12345"
;
Integer change = Integer.valueOf(str);


Code
class
 
Example
 
{

  
public
 
static
 
void
 
main
(String args[])
 
{
    
// String literal

    String str = 
"789"
;

    
// Holds the integer equivalent assuming base 10 interpretation of str

    Integer ans = Integer.valueOf(str);
 
    
// Holds the integer equivalent assuming base 16 interpretation of str

    Integer ans16 = Integer.valueOf(str, 
16
);

     System.out.println(ans);
     System.out.println(ans16);
   }
 }


Output:
789

1929




NumberFormatException in Java
If the string literal provided as an argument is ill-formatted, i.e., contains characters other than numerics, NumberFormatException is thrown. Both the Integer.parseInt() and Integer.valueOf() throw NumberFormatException when the string input contains invalid characters.
Code:
class
 
NumberFormatExceptionExample
 
{

  
public
 
static
 
void
 
main
(String args[])
 
{
    
// Contains characters that cannot be converted to integers

    String str = 
"abc123"
;

    
// throws NumberFormatException

    
int
 ans = Integer.parseInt(str);

    System.out.println(ans + 
"\n"
);
  }
 }


Output:
Exception in thread 
"main"
 java.lang.NumberFormatException: For input string: 
"abc123"

        at java.base/java.lang.NumberFormatException.forInputString(NumberFormatException.java:
65
)
        at java.base/java.lang.Integer.parseInt(Integer.java:
652
)
        at java.base/java.lang.Integer.parseInt(Integer.java:
770
)
        at Main.main(Main.java:
8
)


Important Points

The presence of leading zeroes in the string will not be counted by the
parseInt()
 as well as the 
valueOf()
 method.
The first character as ‘+’ or ‘-’ indicates the sign of the number, which is accepted by both methods of changing the string to integer in java.

Code:
class
 
Example
 
{

  
public
 
static
 
void
 
main
(String args[])
 
{
    
// String with leading zeroes

    String leadingZero = 
"00789"
;

    
// Strings with a sign

    String signConvert = 
"-12"
;

    
int
 ans = Integer.parseInt(leadingZero);
    
int
 ans1 = Integer.parseInt(signConvert);

    System.out.println(ans); 
// outputs 789

    System.out.println(ans1); 
// outputs -12

  }
 }


Output:
789
12

Conclusion


Integer.parseInt()
 converts a String to an int whereas 
Integer.valueOf()
 converts a String to an object of Integer class.
Null, empty, or non-numeric data in a string literal passed as an argument to
parseInt()
 and 
valueOf()
 methods will throw a 
NumberFormatException
.
Overloaded methods of parseInt() and valueOf() can be used to specify the radix of String representation.