What is the equivalent lambda expression for `System.out::println` in Java?

Exploring the Equivalent Lambda Expression for System.out::println

In Java programming, method references offer a concise syntax to invoke methods. One such example is System.out::println, which serves as a shortcut for referring to the println method of the System.out class.

This method reference allows us to write code like this:

numbers.forEach(System.out::println);

where the numbers list contains integers that are printed to the console. However, there is a corresponding lambda expression that achieves the same functionality.

To find this lambda expression, we need to understand how method references work. When using System.out::println, the initial evaluation of System.out yields an instance of PrintStream, which is stored in a lambda expression and used to invoke println.

Directly translating this concept into a lambda expression, we get the following:

numbers.forEach(o -> {
    PrintStream p = Objects.requireNonNull(System.out);
    p.println(o);
});

This lambda expression explicitly retrieves the PrintStream instance and assigns it to the variable p. The placeholder o represents each element of the numbers list.

It's worth noting that this lambda expression is an exact equivalent of System.out::println, capturing the evaluated System.out instance. However, the latter method reference has the advantage of being more concise and readable.

So, while the lambda expression provides a more explicit view of what happens under the hood, the method reference System.out::println remains a valuable syntactic shortcut in scenarios like the one exemplified above.

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