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Ans. Cloneable is a declaration that the class implementing it allows cloning or bitwise copy of it's object state. It is not having any method because it is a MARKER interface.
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Ans. It's a technique to allow multiple clients to make use of a cached set of shared and reusable connection objects providing access to a database or other resource.
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Ans. Volatile is an instruction that the variables can be accessed by multiple threads and hence shouldn't be cached. As volatile variables are never cached and hence their retrieval cannot be optimized.
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Ans. Java is a portable-language because without any modification we can use Java byte-code in any platform(which supports Java). So this byte-code is portable and we can use in any other major platforms.
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If you want to write a checked exception that is automatically enforced by the Handle or Declare Rule, you need to extend the Exception class.
You want to write a runtime exception, you need to extend the RuntimeException class.
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Ans. It is used to sort collections and arrays of objects using the collections.sort() and java.utils. The objects of the class implementing the Comparable interface can be ordered.
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Ans. Externalizable is an interface which contains two methods readExternal and writeExternal. These methods give you a control over the serialization mechanism.
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Ans. String is immutable in java and stored in String pool. Once it's created it stays in the pool until unless garbage collected, so even though we are done with password it's available in memory for longer duration and there is no way to avoid it. It's a security risk because anyone having access to memory dump can find the password as clear text.
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Ans. Since String is immutable, its hashcode is cached at the time of creation and it doesnt need to be calculated again. This makes it a great candidate for key in a Map and its processing is fast than other HashMap key objects. This is why String is mostly used Object as HashMap keys.
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Q288. Will the static block be executed in the following code ? Why ?
class Test { static { System.out.println("Why I am not executing "); } public static final int param=20; }
public class Demo { public static void main(String[] args) { System.out.println(Test.param); } }
Ans. No the static block won't get executed as the referenced variable in the Test class is final. Compiler replaces the content of the final variable within Demo.main method and hence actually no reference to Test class is made.
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Ans. These are the tables that are created temporarily and are deleted once the Stored Procedure is complete.
For example - we may like to pull some info from a table and then do some operations on that data and then store the output in final output table. We can store the intermediary values in a temp table and once we have final output with us, we can just delete it.
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Ans. Compile Time Error: Unhandled exception type Exception
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Q295. Does SQL allow null values ? Can we use it within Where clause ?
Ans. Yes , we can have null values for columns in SQL. Null value represent that the columns value is unknown or haven't been filled. Yes, We can use it within where clause to get the rows with null values.
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Ans. No. It gives the error "Cannot Instantiate the type Calendar". Calendar is an abstract class and hence Calendar object should be instantiated using Calendar.getInstance().
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Which method needs to be implemented if a class is implementing comparable interface ?
