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    <p>Another option by using Copy Constructor (from <a href="http://www.javapractices.com/topic/TopicAction.do?Id=12" rel="noreferrer">Java Practices</a>):</p> <pre><code>public final class Galaxy { public Galaxy (double aMass, String aName) { fMass = aMass; fName = aName; } /** * Copy constructor. */ public Galaxy(Galaxy aGalaxy) { this(aGalaxy.getMass(), aGalaxy.getName()); //no defensive copies are created here, since //there are no mutable object fields (String is immutable) } /** * Alternative style for a copy constructor, using a static newInstance * method. */ public static Galaxy newInstance(Galaxy aGalaxy) { return new Galaxy(aGalaxy.getMass(), aGalaxy.getName()); } public double getMass() { return fMass; } /** * This is the only method which changes the state of a Galaxy * object. If this method were removed, then a copy constructor * would not be provided either, since immutable objects do not * need a copy constructor. */ public void setMass( double aMass ){ fMass = aMass; } public String getName() { return fName; } // PRIVATE ///// private double fMass; private final String fName; /** * Test harness. */ public static void main (String... aArguments){ Galaxy m101 = new Galaxy(15.0, "M101"); Galaxy m101CopyOne = new Galaxy(m101); m101CopyOne.setMass(25.0); System.out.println("M101 mass: " + m101.getMass()); System.out.println("M101Copy mass: " + m101CopyOne.getMass()); Galaxy m101CopyTwo = Galaxy.newInstance(m101); m101CopyTwo.setMass(35.0); System.out.println("M101 mass: " + m101.getMass()); System.out.println("M101CopyTwo mass: " + m101CopyTwo.getMass()); } } </code></pre>
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    1. USMr_and_Mrs_D
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    1. COI wouldn't use getter in the copy constructor. First you don't need them because you have always access to instance variables. Second if you make this yourself a practice you might lower encapsulation by creating too much getters. And finally it can be error prone. Imagine you tweak the value in getMass() than you would copy the tweaked value into the instance variable of the new object which would tweak the value a second time if you call getMass on the new object.
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      1. USNorbert Hartl
 

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