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<p>Use a <a href="http://martinfowler.com/eaaCatalog/unitOfWork.html" rel="nofollow">Unit Of Work</a>. A Unit Of Work is used to determine which entities/objects are "dirty" - meaning their in-memory data is out-of-sync with the persistence store or database - and which are "clean".</p> <p>Just tweak the concept to keep track of which properties are dirty and you're good to go.</p> <h1>Example</h1> <p>(it's been a while since I've written Java and I don't have Java on this machine, so there might be little errors)</p> <h2><code>MyClass.java</code></h2> <pre><code>public class MyClass extends ChangeObservable { private String name; private Age int; public MyClass(name, age) { // when the object is first created, // I'm assuming that the "clean" values are provided this.name = name; this.age = age; } public String getName() { return name; } public void setName(n) { name = n; this.fireChangeEvent("name"); } public String getAge() { return age; } public void setAge(a) { age = a; this.fireChangeEvent("age"); } } </code></pre> <h2><code>UnitOfWork.java</code></h2> <pre><code>public class UnitOfWork implements ChangeListener { // dunno if this is the most efficient implementation... private HashSet<String> dirties = new HashSet<String>(); private Observable obj; public UnitOfWork(Observable obj) { this.obj = obj; obj.registerChangeListener(this); } public void registerDirty(propName) { // probably more code needed... dirties.add(propName); } public HashSet<String> getDirtyProperties() { // probably more code needed... return new HashSet<String>(dirties); } public void onChangeEvent(propName) { this.registerDirty(propName); } // note: a UnitOfWork needs more functionality than this! // I've implemented the bare minimum for the example // but it would also need methods like `registerClean(...)` } </code></pre> <h2><code>Driver.java</code></h2> <pre><code>public class MyDriver { public static void main(String[] argv) { MyClass myObj = new MyClass("Richard", 3); UnitOfWork uow = new UnitOfWork(myObj); myObj.setName("Mark"); for(String propName : uow.getDirtyProperties()) { System.out.print(propName); } } } </code></pre> <p>... now the <code>UnitOfWork.getDirtyProperties(...)</code> can be used to determine which properties are clean and dirty.</p>
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1. POHow to update an arbitrary field in a POJO?
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