-3
As many as you want. Even if it has a theoretical limit it is much larger than the practical.
What exists is only a recommendation for one class per source file.
And this has nothing to do with Eclipse, no matter if you are using this IDE or not. It is a matter of the Java implementation you are using. See What is a programming language, IDE and compiler?.
As far as I know there is no limit, not one that is imposed by language/IDE
– user28595
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– Maniero