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Ram swaroop
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‎_posts/2015-06-30-constructors.md‎

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### Below are the important rules for Constructors:
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__1.__ If you don't type a constructor into your class code, a default constructor will be automatically generated by
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the compiler. The default constructor is ALWAYS a no-arg constructor.
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the compiler. The __default constructor (the one supplied by compiler) is ALWAYS a no-arg constructor__.
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<table>
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</tr>
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</table>
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__2.__ Every constructor has, as its first statement, either a __call to an overloaded constructor (`this()`) or a call to the
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superclass constructor (`super()`)__, and if not it is inserted by the compiler. Remember, compiler __always inserts a _no-arg_
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call to `super()`__, it never passes any arguments.
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<table>
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<tr>
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<td>
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{% highlight java %}
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public class Foo {
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class Foo {
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Foo() { }
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}
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{% endhighlight %}
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</td>
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<td>
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{% highlight java %}
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public class Foo {
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public Foo() {
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class Foo {
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Foo() {
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super();
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}
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}
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{% endhighlight %}
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</td>
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</tr>
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</table>
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__2.__ Every constructor has, as its first statement, either a call to an overloaded constructor (`this()`) or a call to the
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superclass constructor (`super()`), and if not it is inserted by the compiler.
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__3.__ If you want a no-arg constructor and you've typed any other constructor(s) into your class code, the __compiler won't
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provide the no-arg constructor (or any other constructor)__ for you. In other words, if you've typed in a constructor with
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arguments, you won't have a no-arg constructor unless you type it in yourself.
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<table>
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<td>
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{% highlight java %}
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class Foo {
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Foo() { }
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Foo(String s) {
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super();
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}
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}
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{% endhighlight %}
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</td>
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<td>
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Code is the same. Compiler doesn’t insert anything here.
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</td>
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</tr>
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</table>
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__4.__ Constructors can use __any access modifier, including private__. (A private constructor means only code within the
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class itself can instantiate an object of that type, so if the private constructor class wants to allow an instance of
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the class to be used, the class must provide a static method or variable that allows access to an instance created
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from within the class. Moreover, for a Singleton you are bound to make all constructors of class private.)
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<table>
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<tr>
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<td>
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{% highlight java %}
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class Foo {
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Foo() {
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public class Foo {
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}
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{% endhighlight %}
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</td>
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<td>
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{% highlight java %}
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public class Foo {
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public Foo() {
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super();
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}
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}
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{% endhighlight %}
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</td>
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</tr>
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</table>
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__3.__
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<tr>
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<td>
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{% highlight java %}
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private class Foo {
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}
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{% endhighlight %}
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</td>
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<td>
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{% highlight java %}
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private class Foo {
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private Foo() {
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super();
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}
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}
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{% endhighlight %}
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</td>
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</tr>
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</table>
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{% include responsive_ad.html %}
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