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POJava API Example for abstract class. unable to understand the concept properly so reposted
 

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  1. POJava API Example for abstract class. unable to understand the concept properly so reposted
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    <p>I am just trying myself to be comfortable with java api. But I am unable to do it. Not knowing the purpose of when to use abstract class.</p> <p>Consider the java library collections</p> <pre><code> Collections List Set </code></pre> <p>All 3 are interfaces but the major thing , though they have functions which are common that is add , addAll, contains,containsAll etc. List implements in its own and set implements in another way ( telling about duplication ). Set does not allow duplicates list allows duplicates. </p> <p>So what I am trying to say is when ever there is no common features for sub-entity with super-entity we have to go for interface</p> <p>To still more make it clear , if suppose we make Collection as abstract class we need some methods to be properly defined rather than just declared but the functionality of list and set is differnt ( no common definition to bothe) hence they just declared it as interface and made a force rule that both list and set should implement this.</p> <p>But if there is some common functionality which both has then keep it as to be abstract class. </p> <p>So to get an example from Java itself. Lets consider Number class which is made ABSTRACT. Lets see why it could not be done using interface now!!!</p> <pre><code>**public abstract class Number extends Object methods are** </code></pre> <p><strong><code>byte byteValue()</code></strong> Returns the value of the specified number as a byte.</p> <p><strong><code>abstract double doubleValue()</code></strong> Returns the value of the specified number as a double.</p> <p><strong><code>abstract float floatValue()</code></strong> Returns the value of the specified number as a float.</p> <p><strong><code>abstract int intValue()</code></strong> Returns the value of the specified number as an int.</p> <p><strong><code>abstract long longValue()</code></strong> Returns the value of the specified number as a long.</p> <p><strong><code>short shortValue()</code></strong> Returns the value of the specified number as a short.</p> <p>Now here the byteValue is a non-abstract method and other methods XXXValue are abstract. We will see Y???</p> <p>byteValue()</p> <pre><code>// taken from Number class java doc api public byte byteValue() </code></pre> <p>Returns the value of the specified number as a byte. This may involve rounding or truncation.</p> <pre><code>And this byteValue() method is being overriden by all the other classes like Integer,Double,Float etc. </code></pre> <p>Instead they can keep byteValue() also abstract !!! But they dint do it. Wish to know why they have done like this.</p>
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    1. USsai sindhu
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    1. CONot even the mighty gods of software development that are the builders of the Java API are infallible :)
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    2. COWhat is your real question?
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