Java / Eclipse: "Lambda expressions cannot be used in an evaluation expression"

Question

I wrote the following lambda expression

int size = ((List<?>) receipt.getPositions().stream().filter(item -> true).collect(Collectors.toList())).size() 

The variable size calculated correctly!

But when I try to check it ( Ctrl + Shift + I ) or try to see the result of the expression in the expression of the Eclipse expressions, I get the following error:

"Lambda expressions cannot be used in a value expression"

Are there other ways to see the result of such an expression instead of storing it in a variable?

PS: I use Java 8 and Eclipse neon. 2

Answer 1

A simple solution to this is to convert your lambda to create an anonymous class. By creating a variable of the required interface, you get a debug expression.

  Predicate<Object> predicate = new Predicate<Object>() { @Override public boolean test(Object item) { return true; } }; int size = ((List<?>) receipt.getPositions().stream().filter(predicate).collect(Collectors.toList())).size(); 

Now, if you are standing in the line "int size = ..." during debugging, you can view the result of the following:

 ((List<?>) receipt.getPositions().stream().filter(predicate).collect(Collectors.toList())).size() 

Hope this helps :)