#include <iostream>

struct Java_boolean
{
    explicit constexpr Java_boolean( bool b = false ) : value(b) {}

    using Java_bool_t = void (Java_boolean::*)() const ;
    operator Java_bool_t() const { return value ? &Java_boolean::not_integral : nullptr ; }

    int to_int() const { return value ; }
    bool operator== ( Java_boolean that ) const { return value == that.value ; }
    bool operator!= ( Java_boolean that ) const { return value != that.value ; }
    Java_boolean operator! () const { return Java_boolean { !value } ; }

    private:
        bool value ;
        void not_integral() const {}

    template < typename STREAM > inline friend
    STREAM& operator << ( STREAM& stm, Java_boolean b )
    { return stm << "Java_" << ( b.value ? "true" : "false" ) ; }
};

constexpr Java_boolean Java_true { true } ;
constexpr Java_boolean Java_false { false } ;

int main()
{
    Java_boolean flag { Java_true } ;
    if( flag ) std::cout << "ok\n" ;
    if( flag == Java_true ) std::cout << "ok\n" ;
    std::cout << flag << '\n' ;

    int i = flag.to_int() ; // fine
    //int j = flag ; // error

    flag = Java_boolean(i) ; // fine
    // flag = i ; // error
}