How to Convert String to Integer Using Java 8 with Integer::valueOf

Learn how to convert String to Integer using Java 8 with Integer::valueOf method reference and functional interface example with output.

Code Explanation (Step-by-Step) :-

  • Convertor is a Functional Interface that defines one method to convert a value from one type to another.
  • In this program, the input type is String , and the output type is Integer.
  • Integer::valueOf is used as a method reference to convert the given String into an Integer.
  • The method interface is assigned to the convert() method of the Convertor interface.
  • When con.convert(“123”) is called, it internally calls Integer.valueOf(“123”).
  • The returned Integer value is stored in the value variable.
  • Finally, the program prints the converted integer value 123.
				
					@FunctionalInterface
interface Convertor<F, T> {
	T convert(F from);
}

public class TestStream {
	public static void main(String[] args) {
		Convertor<String, Integer> con = Integer::valueOf;
		Integer value = con.convert("123");
		System.out.println(value);
	}
}

Output :- 123

Difference Between Integer::valueOf and Integer.parseInt() –

  1. Return Type
  • Integer::valueOf returns an Integer object.
  • Integer.parseInt() returns a primitive int value.
  1. Usage
  • Integer::valueOf is commonly used when an object is needed.
  • Integer.parseInt() is used when a primitive integer is enough.
  1. Java 8 Method Reference Support
  • Integer::valueOf can be used directly as a method reference in Java 8.
  • Integer.parseInt() can also be used as a method reference, but it returns int instead of Integer.
  1. Performance
  • Integer.parseInt() is slightly more efficient when you only need a primitive int.
  • Integer::valueOf may involve object creation or caching, so it is useful when working with objects.
  1. Use Case
  • Use Integer::valueOf when working with collections, generics, or functional interfaces that require Integer.
  • Use Integer.parseInt() when you only need a numeric primitive value for calculations.

FAQ :
Can Integer::valueOf throw an exception?
Yes, it throws NumberFormatException if the input String contains invalid numeric data.

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