Error in Types in Lamdba Expressions Java and Stream

Asked Jun 20 '21 at 18:59

Active Jun 20 '21 at 19:05

Viewed 22 times

I'm learning how Streams work in java and I found some examples, but when I am trying to run this, this throws some exceptions because the lambda expressions. I would like to understand why.

import java.util.Arrays;
import java.util.List;
import java.util.stream.Collectors;

public class StreamExample {

    public static void main (String[] args) {
        
        List number = Arrays.asList(2, 3, 4, 5);
        List square = number.stream().map(x-> x*x).collect(Collectors.toList());

        List names = Arrays.asList("Reflection","Collection","Stream");
        List result = names.stream().filter(s->s.startsWith("S")).collect(Collectors.toList());
        
    }
}

I get these two errors.

Operator '*' cannot be applied to 'java.lang.Object', 'java.lang.Object'
Cannot resolve method 'startsWith' in 'Object'

Thanks for the help

asked Jun 20 '21 at 18:59

YGz

1

You are using raw types. Everywhere. Don’t. Especially not with feature that rely heavily on type inference to be useful. – Boris the Spider Jun 20 '21 at 19:02
Also you need to learn early the difference between _compiler errors_ and _exceptions_ (which happen when you run your code). – chrylis -cautiouslyoptimistic- Jun 20 '21 at 20:25

Error in Types in Lamdba Expressions Java and Stream

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