java - Private Interfaces -

how can use methods of private interface in our code?

abstract classes cannot instantiated. so, if need use methods of abstract class, can inherit them , use methods.

but, when talk interfaces, need implement them use methods.

the private keyword means "anyone in same class":

public class foo {     private interface x {...}    private class x1 implements x {...} }

this means classes declared inside of foo can use interface foo.x.

a common use case command pattern foo accepts, say, strings , converts them internal command objects implement same interface.

if add second class bar file foo.java, can't see foo.x.

Error