A method for managing a device implementing a Java Card environment, said device comprising an operational applet and a personalisation applet which are Java-based applications stored respectively in a first package and in a second package, said first and second packages being separated by Java Card firewalls, said method comprising: - receiving, by the operational applet, at least one personalisation command and forwarding said at least one personalisation command to the personalisation applet; - generating, by the personalisation applet, personalisation instructions by processing the at least one personalisation command; - sending, by the personalisation applet, the personalisation instructions to the operational applet; - performing, by the operational applet, a personalisation of the first package based on the personalisation instructions received from the personalisation applet, thereby rendering operational the operational applet by said device for performing at least one function; and - deleting, by a management applet of the device, the second package upon detection that the personalisation is completed, wherein the operational applet and the personalisation applet communicate with each other using respective Java Card interfaces implemented in a third package separated from the first and second packages by Java Card firewalls, wherein the method comprises, before the operational applet receives the personalisation command: - storing said first, second and third packages in said device and forming Java Card firewalls separating each of said first, second and third packages, wherein said third package comprises: - a first Java Card interface called by the operational applet to forward the at least one personalisation command to the personalisation applet; - a second Java Card interface called by the personalisation applet to send the personalisation instructions to the operational applet; and - a library of public classes accessed by the personalisation applet and by the operational applet. - receiving, by the operational applet, at least one personalisation command and forwarding said at least one personalisation command to the personalisation applet; - generating, by the personalisation applet, personalisation instructions by processing the at least one personalisation command; - sending, by the personalisation applet, the personalisation instructions to the operational applet; - performing, by the operational applet, a personalisation of the first package based on the personalisation instructions received from the personalisation applet, thereby rendering operational the operational applet by said device for performing at least one function; and - deleting, by a management applet of the device, the second package upon detection that the personalisation is completed, wherein the operational applet and the personalisation applet communicate with each other using respective Java Card interfaces implemented in a third package separated from the first and second packages by Java Card firewalls, wherein the method comprises, before the operational applet receives the personalisation command: - storing said first, second and third packages in said device and forming Java Card firewalls separating each of said first, second and third packages, wherein said third package comprises: - a first Java Card interface called by the operational applet to forward the at least one personalisation command to the personalisation applet; - a second Java Card interface called by the personalisation applet to send the personalisation instructions to the operational applet; and - a library of public classes accessed by the personalisation applet and by the operational applet. wherein the operational applet and the personalisation applet communicate with each other using respective Java Card interfaces implemented in a third package separated from the first and second packages by Java Card firewalls, wherein the method comprises, before the operational applet receives the personalisation command: - storing said first, second and third packages in said device and forming Java Card firewalls separating each of said first, second and third packages, - storing said first, second and third packages in said device and forming Java Card firewalls separating each of said first, second and third packages, wherein said third package comprises: - a first Java Card interface called by the operational applet to forward the at least one personalisation command to the personalisation applet; - a second Java Card interface called by the personalisation applet to send the personalisation instructions to the operational applet; and - a library of public classes accessed by the personalisation applet and by the operational applet. - a first Java Card interface called by the operational applet to forward the at least one personalisation command to the personalisation applet; - a second Java Card interface called by the personalisation applet to send the personalisation instructions to the operational applet; and - a library of public classes accessed by the personalisation applet and by the operational applet.