ValueOf() Method in Java

In this guide, we will discuss one of the most commonly used method in Java. The valueOf() method is available in several wrapper classes and other classes such as String class. This method is mostly used in the conversion of types, for example, converting int to Integer, double to Double etc.

ValueOf() method usage In Wrapper Classes

In wrapper classes, the valueOf() method is used for converting primitive types such as int, float double to Wrapper class objects such as Integer, Float, Double etc.

Integer.valueOf()

Converts a primitive int or a String to an Integer object.

public class ValueOfExample {
    public static void main(String[] args) {
        // From int to Integer
        Integer intObj1 = Integer.valueOf(101);  

        // From String to Integer      
        Integer intObj2 = Integer.valueOf("200");      

        System.out.println(intObj1);  // Output: 101
        System.out.println(intObj2);  // Output: 200
    }
}

Double.valueOf()

Converts a primitive double or a String to a Double object.

public class ValueOfExample {
    public static void main(String[] args) {
        // From double to Double
        Double doubleObj1 = Double.valueOf(10.55);    
 
        // From String to Double    
        Double doubleObj2 = Double.valueOf("20.55");      

        System.out.println(doubleObj1);  // Output: 10.55
        System.out.println(doubleObj2);  // Output: 20.55
    }
}

Boolean.valueOf()

Converts a primitive boolean or a String to a Boolean object.

public class ValueOfExample {
    public static void main(String[] args) {
        // From boolean to Boolean
        Boolean boolObj1 = Boolean.valueOf(true);   

        // From String to Boolean     
        Boolean boolObj2 = Boolean.valueOf("false");     

        System.out.println(boolObj1);  // Output: true
        System.out.println(boolObj2);  // Output: false
    }
}

ValueOf() method In the String Class

In the String class, the valueOf() method is used to convert various data types into their string representation.

Example of conversion from different data type to String

public class ValueOfStringExample {
    public static void main(String[] args) {
        // int to String Conversion
        String str1 = String.valueOf(100);
        System.out.println(str1);  // Output: "100"

        // double to String Conversion
        String str2 = String.valueOf(10.5);
        System.out.println(str2);  // Output: "10.5"

        // boolean to String Conversion
        String str3 = String.valueOf(true);
        System.out.println(str3);  // Output: "true"

        // char array to String Conversion
        char[] charArray = {'J', 'a', 'v', 'a'};
        String str4 = String.valueOf(charArray);
        System.out.println(str4);  // Output: "Java"

        // Object to String Conversion
        Object obj = new Object();
        String str5 = String.valueOf(obj);
        System.out.println(str5);
    }
}

Points to Note:

1. Overloading of valueOf() Method: The valueOf() method is overloaded in wrapper classes and String class to handle different input types (e.g., primitive types and strings).
2. Used for Conversion: It provides an easy way to convert primitive data types to Wrapper objects as well as other data types to Strings.
3. Handles Null Input: In case of wrapper classes, if the input is null, it throws NumberFormatException. In case of String class, String.valueOf(null) returns the string “null” if the input data is null.