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    <p>Question 1 - Basic Java Classes:</p> <p>There's pretty much only 3 things you're going to find in a Java class</p> <ul> <li>Field/attribute (Depending on your language of origin)</li> <li>Method</li> <li>Constructor (Which looks like a special kind of method)</li> </ul> <p>Every class is going to have a class name that shares the name of the file it's located in. So to expand Money out a bit:</p> <pre><code>Money.java ---------- public class Money { // This is a field/attribute Long value; // This is a constructor public Money() { this.value = Long(0L); } // This is a method public Long getValue() { return value; } // Another method public void makeMoney(Long moreMoney) { this.value = this.value + moreMoney; } } // Everything in here is part of the Money class </code></pre> <p>The only distinction between a constructor and a method is that a constructor has no specified return value, which is declared as a type right before the name of a potential method. Constructors do have to be named the same as the class they are contained in, but why is implied in how they are written. </p> <p>Another way of looking at it is if you remove all of the non-type related Java keywords (public, private etc., but not things like float and int) from the front of the method you're looking at (A list of which you can find <a href="http://docs.oracle.com/javase/tutorial/java/nutsandbolts/_keywords.html" rel="nofollow">here</a>), is there anything left in front of the method?</p> <p>With the Money we have at the moment, it would look like this:</p> <ul> <li>Money()</li> <li>Long getValue()</li> <li>void makeMoney()</li> </ul> <p>The constructor is the one that has no type for the return value, because it is implied in the declaration.</p> <p>Question 2/3 - Get/Set methods:</p> <p>I'm going to say something potentially controversial, but don't worry about these yet. Get/Set are essentially patterns for Object Oriented development, and generally good Java style, but they aren't required (Last I checked, Android development actually discourages their use when possible for optimization reasons). Moreover, not all fields in your objects will be accessible or mutable so writing them isn't mandatory.</p> <p>If you declare all of your fields as public (Like the 'value' field is implied to be right now), you simple can do this:</p> <pre><code>Money myMoney = new Money(new Long(40L)); System.out.println(myMoney.value) // 40 myMoney.value = new Long(20L); System.out.println(myMoney.value) // 20 </code></pre> <p>Aside from that, the notion of get() and set() are just methods. There is nothing special about them at all. The main reason they exist is because for general Object-Oriented programming, you shouldn't have to directly modify the internal workings of an object (This is <a href="http://en.wikipedia.org/wiki/Encapsulation_%28object-oriented_programming%29" rel="nofollow">the principle of Encapsulation</a>). Everything you should need to affect state or get something out of it should be handled by a method.</p> <p>In a pithy one-liner: If you need to know the fields of an object to use it, you designed it incorrectly.</p> <p><em>Big Picture</em> So what get() and set() really are is a pair of commonly written methods that happen to affect a field in an object in an extremely simple way (get() is a simple access to a field, set() is assignment to that field). It's just that other methods you write will happen to do more complicated stuff than that.</p>
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