Java String to int

Last Updated : 17 Feb 2026

In Java, the conversion of a String variable into an int variable is considered a common process or operation. It may occur when the user's input is processed or manipulated. We can convert a String to an int in Java using the Integer.parseInt() and Integer.valueOf() methods. These methods return instances of the Integer class.

When to Use String to int Conversion?

It is generally used if we have to perform mathematical operations on a string that contains a number. Whenever we receive data from a TextField or TextArea, the entered data is received as a string. If the entered data is in number format, we need to convert the string to an int. To do so, we use the Integer.parseInt() method.

Using Integer.parseInt(String str) Method

The method parses the string argument as a signed decimal integer. 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.

The resulting integer value is returned, exactly as if the argument and the radix 10 were given as arguments to the parseInt(java.lang.String, int) method. It throws a NumberFormatException if the string does not contain a parsable integer.

Syntax:

Example: Integer.parseInt(String str) Method

Example

public class Main {
    public static void main(String[] args) {
        String numberString = "2025";
        int number = Integer.parseInt(numberString);
        System.out.println("Parsed integer: " + number);
    }
}

Compile and Run

Output:

Parsed integer: 2025

Explanation

The above program takes the string "2025" and converts it into the integer 2025 using Integer.parseInt(). It's especially useful when we are reading numbers from user input or files where values are stored as strings.

Using Integer.parseInt(String str, int radix) Method

The method parses the string as a signed integer for the first argument and an integer in the specified radix for the second argument. The default radix value used in Java is 10, if not specified. The characters in the string must all be digits of the specified radix, except for the first character. The first character may be a + or - sign that represents a positive or negative value. The method returns an integer value as a result.

It throws a NumberFormatException if any of the following situation occurs:

The first argument is null or the string length is zero.
The radix is either smaller than Character.MIN_RADIX or larger than Character.MAX_RADIX.
Any character of the string is not a digit of the specified radix, except that the first character may be a minus sign '-' ('\u002D') or plus sign '+' ('\u002B') provided that the string is longer than length 1.
The value represented by the string is not a value of type int.

Syntax:

public static int parseInt(String s, int radix) throws NumberFormatException

Examples

Method	Returns
parseInt("0", 10)	0
parseInt("473", 10)	473
parseInt("+42", 10)	42
parseInt("-0", 10)	0
parseInt("-FF", 16)	-255
parseInt("1100110", 2)	102
parseInt("2147483647", 10)	2147483647
parseInt("-2147483648", 10)	-2147483648
parseInt("2147483648", 10)	throws a NumberFormatException
parseInt("99", 8)	throws a NumberFormatException
parseInt("PERL", 10)	throws a NumberFormatException
parseInt("Kona", 27)	411787

Example: Integer.parseInt(String str, int radix) Method

Example

public class Main {  
    public static void main(String[] args) {          
        int x = Integer.parseInt("101", 2);  
        int y = Integer.parseInt("+300", 16);  
        int z = Integer.parseInt("-950", 12);    
        int a = Integer.parseInt("0", 10);  
        int b = Integer.parseInt("225", 10); 
        int c = Integer.parseInt("+63", 10); 
        int p = Integer.parseInt("-0", 10);      
        int q = Integer.parseInt("-FD", 16);   
        int r = Integer.parseInt("11001100", 2);
        int t = Integer.parseInt("2147483647", 10);
        int u = Integer.parseInt("-2147483648", 10);
        //int v = Integer.parseInt("2147483648", 10);
        //int k = Integer.parseInt("99", 8);
        //int l = Integer.parseInt("PERL", 10);
        int m = Integer.parseInt("Kona", 27);  
        System.out.println("x = "+x);  
        System.out.println("y = "+y);  
        System.out.println("z = "+z); 
        System.out.println("a = "+a);  
        System.out.println("b = "+b);  
        System.out.println("c = "+c);  
        System.out.println("p = "+p);  
        System.out.println("q = "+q);  
        System.out.println("r = "+r);  
        System.out.println("t = "+t);  
        System.out.println("u = "+u);  
        //System.out.println("v = "+v);  
       // System.out.println("k = "+k);  
        //System.out.println("l = "+l);  
        System.out.println("m = "+m);   
    }  
}  

Compile and Run

Output:

x = 5
y = 768
z = -1356
a = 0
b = 225
c = 63
p = 0
q = -253
r = 204
t = 2147483647
u = -2147483648
m = 411787

In the above program, note that the variables v, k, and l are comments because they throw NumberFormatException. You can check by removing the comments.

Using Integer.valueOf() Method

The Integer.valueOf() method in Java is a static method used to convert a value-either a primitive int or a String-into an Integer object. It is a part of the java.lang.Integer class is often used when we need an Integer object rather than a primitive int. The method has the following three overloaded variants:

valueOf(int i): It converts a primitive int to an Integer object.
valueOf(String s): The method parses the string and returns an Integer object. Throws NumberFormatException if the string is not a valid integer.
valueOf(String s, int radix): It parses the string using the specified radix (base) and returns an Integer object.

Example of Integer.valueOf() Method

Example

//Java Program to demonstrate the conversion of String into Integer using Integer.valueOf() method  
public class Main {  
    public static void main(String args[]) {  
        //Declaring a string  
        String s="200";  
        //converting String into Integer using Integer.valueOf() method  
        Integer i=Integer.valueOf(s);  
        System.out.println(i);  
    }
}  

Compile and Run

Output:

NumberFormatException Case

If we do not have numbers in a string literal, call Integer.parseInt() or Integer.valueOf() methods throw NumberFormatException.

Example

// Java Program to demonstrate the case of NumberFormatException  
public class Main {  
    public static void main(String args[]) {  
        String s="hello";  
        int i=Integer.parseInt(s);  
        System.out.println(i);  
    }
}  

Compile and Run

Output:

Exception in thread "main" java.lang.NumberFormatException: For input string: "hello"
at java.base/java.lang.NumberFormatException.forInputString(NumberFormatException.java:67)
at java.base/java.lang.Integer.parseInt(Integer.java:662)
at java.base/java.lang.Integer.parseInt(Integer.java:778)
at Main.main(Main.java:5)

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