parseInt() Method in Java

Syntax of parseInt() in Java

The syntax of parseInt() in java are:-

public static int parseInt(String str)
public static int parseInt(String str, int radix)
public static int parseInt(CharSequence seq, int startIndex, int endIndex, int radix)

Parameters list of Java integer parseInt()

The parameter list of parseInt() is given in the table below.

Return values of the respective parseInt() variants

If a radix is specified in the parseInt() method, an integer value with the corresponding base (can be either two as in binary, 8 as in octal, or 10 as in decimal, or 16 as in hexadecimal) is returned. Else integer value in its decimal number system is returned as the default.

Example

• Java

Java

class Example {  
    public static void main(String[] args) {  
    String str = "717";
    int num = Integer.parseInt(str);
    System.out.println(num + 3); 
    }  
}  

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Output:

720

Thus extracting numerical data from user input or files becomes more effortless. The parseInt() in Java is a pre-defined method in Java that is a part of the Integer class, which belongs to Java.lang package

Working of parseInt() method 

As discussed earlier, the parseInt() method converts a string value to an integer value. But how does it do so? Lets us discuss the working of the Java Integer parseInt() method.

1. The parseInt() method first takes a string as input.

2. In the second step, it checks the first character of the input string to determine the sign (positive or negative).

3. If the first character is identified as a sign, it is removed from the string.

4. The method then iterates through the remaining string and converts each character to its corresponding integer value.

5. If a character in the string turns out to be a letter or a symbol, an exception is thrown.

6. After converting the entire string, an integer value is returned.  

Types of parseInt Java methods

There are three types of parseInt() Java methods.

parseInt( String str)

This method converts a string value to a signed decimal int object. The string's first character may be a "+" or a "-" sign. The characters in the string should not include any letters or other symbols.

parseInt(String str, int radix)

This method converts a string value to a signed decimal int object of a particular number system known as radix. The radix's value can be either 2 as binary, 8 as octal, 10 as decimal, or 16 as hexadecimal. The default radix value used in Java is 10 if nothing is specified. The string's first character may be a "+" or a "-" sign. The characters in the string should not include any letters or other symbols.

parseInt(CharSequence seq, int startText, int endText, int radix)

This method converts the character sequence passed as an argument into a signed integer of a specified number system. The method has two extra parameters, the start index and end index, which specify the section of the character sequence to be parsed.

Implementation of parseInt() methods

The implementation of the parseInt() methods is explained better in the examples below. 

Example 1

• Java

Java

public class Example1 {  
    public static void main(String[] args) {  
        int decimalNum = Integer.parseInt("100");  
        int signedPositiveNum = Integer.parseInt("+20");  
        int signedNegativeNum = Integer.parseInt("-25");  
          
        System.out.println(decimalNum + signedPositiveNum * signedNegativeNum);  
    }  
} 

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Output:

-400 

Example 2

• Java

Java

public class Example2 {  
    public static void main(String[] args) {  
        String str= "250";    
        int num=Integer.parseInt(str, 6);    
        System.out.println(str+100);   
        System.out.println("num = "+num);   
        System.out.println(num+100);    
    }  
}  

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Output:

250100
num = 102
202

Example 3

• Java

Java

public class Example3 {  
    public static void main(String[] args) {          
    	int x = Integer.parseInt("100", 2);  
    	int y = Integer.parseInt("+280", 16);  
    	int z = Integer.parseInt("-350", 12);        
        System.out.println("x = "+x);  
        System.out.println("y = "+y);  
        System.out.println("z = "+z);  
    }  
}  

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Output:

x = 4
y = 640
z = -492

Handling Errors and Exceptions in parseInt Java method

The following exceptions are thrown if the conventions are not followed while using the parseInt java method.

1. If the string parameter contains a null value, a NullPointerException is thrown. 
 

2. A NumberFormatException is encountered if:

• The string parameter passed does not include a valid number except the first character, which can be a "+" or "-" symbol.
• The radix specified is less than the Character.MIN_RADIX
• The radix specified is greater than the Character.MAX_RADIX
  Note: Character.MIN_RADIX = 2 and Character.MAX_RADIX = 36
   

3. The IndexOutOfBoundsException is thrown when

• startIndex is negative
• startIndex is greater than endIndex
• endIndex is greater than the length of CharSequence or the string

Comparisons with other conversion methods

Ninja's toolkit for using the parseInt method in Java

Some of the best practices while using the parseInt java method are:

• Passing the radix as the parameter to the method is always recommended. If it is not specified, the compiler assumes a default value of 10.
   
• There is always a possibility for the program having the parseInt() to throw a NumberFormatException. Thus it is advised to handle the exceptions properly to prevent the program from crashing. You can also use the try-catch blocks to handle the exceptions.
   
•  Check for the null or empty strings to avoid null pointer exceptions.

Advantages of the parseInt() in Java

The advantages of using parseInt() in Java are:

• String to integer conversions: The parseInt method makes the conversion of string value from user input to integer value easier. 
   
• Base conversion: The java method also allows the conversion of the number to a specific radix. Thus conversion to binary and hexadecimal becomes simpler.
   
• Error Handling: An exception of NumberFormatException is encountered if the string is invalid or cannot be converted to an integer. Thus debugging and error handling is done smoothly.
   
• Consistency: The parseInt java method follows the standard Java naming convention for methods and hence is easy to recognize and use in programs. Its consistency in different platforms and versions of Java makes it a reliable and safe method for conversions.

Must Read Type Conversion in Java

Frequently Asked Questions

What is parseInt() in Java?

parseInt() in Java converts a string representation of a number into an integer.

When can the parseInt() method be used?

parseInt() is used when converting string inputs to integers is required, such as handling user input or parsing numeric data from files.

How to convert "123" to 123 in Java?

To convert "123" (string) to 123 (integer) in Java, use Integer.parseInt("123").

Why do we use parseInt()?

parseInt() is used to transform string representations of numbers into integers for arithmetic operations or data processing in Java programs.

Conclusion

We discussed the implementation of the parseInt Java method along with some examples. The article also highlighted the advantages of using the parseInt() method.
We hope this blog has helped you understand the use of the parseInt Java method. Keep feeding curiosity. Explore more of our articles on other topics of Java, such as

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