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Ans. Abstract means that the class is only meant to be subclassed whereas final means that it cannot be subclassed so both concepts - abstract and final are actually mutually exclusive and hence not permitted together.
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Ans. Better Control - If the value is being used at multiple locations , that can be controlled better from single place. Any change would only require making single change.
Meaning , Aliasing and Better Readability - Sometimes its easy to read the value by its meaning or alias ( 0 as ZERO or 0 as NEUTRAL_VALUE ).
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Ans. finally will execute in all graceful situations - graceful executions as well as graceful exceptions. The only situation when finally block won't execute is when the app is abruptly stopped, killed or unplugged.
Q36. If we have to maintain a value "7" denoting "number of days in a week" as constant variable, Which of the following is the best constant name and Why ?
Constant should be such that it uniquely identifies the value it holds and context of the value. SEVEN uniquely identifies the value but doesn't express the context.
Though NUMBER_OF_DAYS_IN_WEEK and NUMBER_OF_DAYS_IN_WEEK_7 makes sense in terms of unique value identification and context but 7 at the end of constant name appears useless as all weeks have 7 days and hence it's the only value it can hold. If it would have been "number of days in a month", it would have made sense to include number of days at the end like
Q37. If we have to maintain a value "31" denoting "number of days in a month" as constant variable, Which of the following is the best constant name and Why ?
Constant should be such that it uniquely identifies the value it holds and context of the value. THIRTY_ONE uniquely identifies the value but doesn't express the context. NUMBER_OF_DAYS_IN_MONTH expresses the context but doesn't specify the value clearly as different month can have different number of days.
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Ans. Objective of constant variable is to provide a context to the value and provide a single point of change. In terms of context, i don't see much need for having constant name for null as null is already self explanatory. In terms of providing single point of change, it doesn't make much sense as it would necessitate that all such placeholders either hold null or a common value.
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Q40. Which of following is / are valid static final declaration ?
public static final String MAX_NUM = "10";
public static final Object NULL = null;
public static final MathContext MATH_CONTEXT = new MathContext(2,RoundingMode.CEILING);
Ans. Yes, it will compile without error. final in this context means that the reference hm cannot be assigned to a new hash map but didn't restrict from changing the state of collection already held by hm.
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Ans. Being final in the sense of objects or object reference means that the reference cannot be reassigned to a different object whereas being immutable means that the object contents cannot be changed.
Strings in Java are immutable.
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Q45. How different is it when final applied to variables and object references ?
Ans. The regular behavior of exception handling will occur. It will look for any immediate catch handler and if none is provided, it would be transmitted to the callers until a catch handler is found or it's out of main function.
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Ans. Returning from inside a finally block will cause exceptions to be lost. A return statement inside a finally block will cause any exception that might be thrown in the try block to be discarded.
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