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:: is called Method Reference. It is basically a reference to a single method. i.e. it refers to an existing method by name.

Short Explanation:
Below is an example of a reference to a static method:

E.g. instead of writing the lambda body

The only major criterion to satisfy is: the method you provide should have a similar signature to the method of the functional interface you use as object reference.

square expects an argument and returns a double. The get method in Supplier returns a value but does not take an argument. Thus, this results in an error.

A method reference refers to the method of a functional interface. (As mentioned, functional interfaces can have only one method each).

Some more examples: the accept method in Consumer takes an input but doesn't return anything.

Above, getRandom takes no argument and returns a double. So any functional interface that satisfies the criteria of: take no argument and return double can be used.

For further reference, see http://cr.openjdk.java.net/~briangoetz/lambda/lambda-state-final.html.

:: is called a method reference. It is basically a reference to a single method. I.e., it refers to an existing method by name.

Short Explanation:

Below is an example of a reference to a static method:

E.g., instead of writing the lambda body

The only major criterion to satisfy is: the method you provide should have a similar signature to the method of the functional interface you use as object reference.

square expects an argument and returns a double. The get method in Supplier returns a value, but it does not take an argument. Thus, this results in an error.

A method reference refers to the method of a functional interface. (As mentioned, functional interfaces can have only one method each.)

Some more examples: the accept method in Consumer takes an input, but it doesn't return anything.

Above, getRandom doesn't take any argument and returns a double. So any functional interface that satisfies the criteria of: take no argument and return double can be used.

For further reference, see State of the Lambda .

:: is called Method Reference. It is basically a reference to a single method. I.e. it refers to an existing method by name.

:: is called Method Reference. It is basically a reference to a single method. i.e. it refers to an existing method by name.

square expects an argument and returns a double. The get method in Supplier expects an argument but doesn't return anything. Thus, this results in an error.

square expects an argument and returns a double. The get method in Supplier returns a value but does not take an argument. Thus, this results in an error.