& Classes Interfaces
Minimizing Accessibility and Security Holes
Introduction
Classes and Interfaces are the backbone of Java Good design = usable, robust, and flexible 1. Minimize accessibility 2. Use private data members w/ accessors
Minimize Accessibility of Classes and Members
Information hiding degree to which the module hides internal data Use multiple modules and keep them hidden!
Advantages of multi-hidden modules
Allows modules to be developed, tested, optimized, and modified individually > SPEED. Eases maintenance > will not harm other modules.
Access Control Mechanisms
Private Protected Public
Rules of Accessibility
Make each class or member as inaccessible as possible. TopLevel classes and interfaces = package private or public If a method overrides supermethod, it cannot have lower level accessibility (compiler will catch this) Public should classes rarely have public fields. Except for public static finals.
Example
Nearly always wrong to have public static final array field //potential security hole Public static final Type[] VALUES = {...};
Better Version: Private static final Type[] PRIVATE_VALUES = {...}; Public static final List VALUES = Collections.unmodifiableList(Arrays.asList(PRIVATE_VA LUES));
Use Private data w/ Accessor methods
Use synchronized methods to protect data from corruption. Multi threads may result in altering members concurrently.
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