Why does lambda translation need generation of a static method?

Question

Lambda translation is a two step process, One: desugaring the lambda into a static method in same class.

public class Main {
    public stat         


        

Answer 1

Your test is incomplete.

public class Lambda {

  private String hello = "Hello from instance";

  public static void main(String[] args) {
    Runnable r = () -> System.out.println("Hello");
    for (Method m: Lambda.class.getDeclaredMethods()) {
      System.out.println(m);
    }
  }

  public void instanceMethodWithAccessToInstanceVariables(){
    Runnable r = () -> System.out.println(hello);
  }

  public void instanceMethodWithoutAccessToInstanceVariables(){
    Runnable r = () -> System.out.println("Hello from instance");
  }
}

This results in the following:

public void Lambda.instanceMethodWithAccessToInstanceVariables()
public void Lambda.instanceMethodWithoutAccessToInstanceVariables()
private static void Lambda.lambda$instanceMethodWithoutAccessToInstanceVariables$2()
private void Lambda.lambda$instanceMethodWithAccessToInstanceVariables$1()
private static void Lambda.lambda$main$0()
public static void Lambda.main(java.lang.String[])

This clearly shows several cases:

• lambdas in static method declare static method
• lambdas in instance methods using instance variables declare instance methods
• lambdas in instance methods not using instance variables declare static method

The two first are rather logical. Why would you expect a static member to access an instance member? Same for the instance method.

The real question is why does an instance method not using any instance variables declare a static method?

Well, this is also for performance and safety reasons mentioned by Tagir.