Have look at the Java Language Specification:
15.27.4. Run-time Evaluation of Lambda Expressions
At run time, evaluation of a lambda expression is similar to evaluation of a class instance creation expression, insofar as normal completion produces a reference to an object. Evaluation of a lambda expression is distinct from execution of the lambda body.
Either a new instance of a class with the properties below is allocated and initialized, or an existing instance of a class with the properties below is referenced.
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These rules are meant to offer flexibility to implementations of the Java programming language, in that:
A new object need not be allocated on every evaluation.
Objects produced by different lambda expressions need not belong to different classes (if the bodies are identical, for example).
Every object produced by evaluation need not belong to the same class (captured local variables might be inlined, for example).
If an "existing instance" is available, it need not have been created at a previous lambda evaluation (it might have been allocated during the enclosing class's initialization, for example).
In principle, this implies that even a single occurrence of Integer::parseInt in your source code may lead to different object instances (even of different classes) when being evaluated multiple times, not to speak of multiple occurrences of it. The exact decision is left to the actual JRE implementation. See this answer discussing the current behavior of Oracle’s implementation.
