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Ans. Yes, doesn't provide exclusive access as we cannot allocate and deallocate memory exclusively as Java internally manages it. The advantage of this is that it relieves the coder for such tasks and helps protect from many bugs that may get introduced with imperfect coding. Moreover as java garbage collector collects all unclaimed memory or objects, it helps the application from memory leaks.
On the flip side , as coder doesn't have extensive excess to memory , it is upto java to decide on the state for programming construct and data storage and hence may introduce some security risks. For example - Java keeps string literals in string pool and there is no exclusive way to remove it and hence may stay and sensitive data in string pool may introduce security issues. Moreover when we overwrite a value or object for a variable / reference, it is upto java to purge those values and hence it may stay in memory for a while till java decide that it is no longer referenced and hence should be removed and hence makes it vulnerable for inappropriate access.
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LikeDiscussCorrect / Improve disadvantages of garbage collection advantages and disadvantages of java memory management java for security applications java with sensitive data memory management
Q423. What is event handling ? What is event propagation ?
Q424. 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. assertThat is introduced with Junit4 and offers many advatanges over assert. Messages are more explanatory, offer better type safety and are more readable. Moreover hamcrest library is portable as it can used both with junit and TestNG.Moreover assertThat provides flexibility as the same method can be used for assert , assertEquals,assertTrue etc through the use of matcher methods.
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Ans. There are 2 ways to specify dependencies in Spring, one by the way of specifying beans in config files and other is by specifying annotations like @Bean, @Component , @Service etc to let spring know of the dependencies.
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Ans. String Pool makes Java more memory efficient by providing a reusable place for string literals. It might be a little performance inconvenience but results in good amount memory saving.
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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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Q433. 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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Q434. 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
Ans. Public constructor is simple and easy as it's the default way of object creation. So there are no additional coding overheads as compiler provides the default constructor if none is provided by coder.
With static final methods, it facilitates loose coupling by segregating the responsibility of object creation to a separate method. Validation can be done on the constructor arguments before calling it. Moreover if any adaption on the arguments is required that can achieved easily with factory method.On the flip side, there is coding overhead and additional method call.
Ans. mutual exclusion i.e the resource is not shareable and hence a process should have exclusive access to it at a particular time
Hold and Wait i.e the process doesn't release all existing resources held by it before requesting for another one.
No preemption i.e noone can forcefully release a resource held by another process and the process should voluntarily release the resource held by it.
Circular Wait - For ex, P1 is waiting on resource to be released by P2, P2 is waiting on resource to be released by P3 and P3 is waiting on the resource to be released by P1
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Ans. Enumeration can iterate only legacy collections like Vector , HashTable and Stack whereas Iterator can iterate both legacy and non legacy collections.
Enumeration is less safer than Iterator
Enumeration is fail safe whereas Iterator is fail fast
Iterator allows for removal of element while traversal whereas Enumeration doesn't have remove method.
Enumerations were introduced in Java 1 whereas Iterators were introduced with Java 2
Enumerations have methods like hasMoreElements and nextElement whereas Iterators have methods like hasNext, next and remove
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Ans. It introduces a layer of adaptations before it reaches the final and desired interface.
Moreover sometimes all requests are forwarded to adapter class. Some of such requests doesn't even require any sort of adaptions as they are qualified to call the final interface directly and introducing overheads.
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Ans. Such a class still can have member elements which can be inherited and hence facilitate code reuse. Moreover Abstract class can have non final static elements whereas interfaces are only allowed to have static final elements.
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Ans. It is used for intercepting the request. It's primary use is to implement security policy. All or specific request types can be intercepted and hence forwarded to authentication / authorization module so as to facilitate authorized requests to application.
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Ans. Hibernate mapping configurations are used for mapping hibernate entities and corresponding DB Tables. Conventionally Entities and Table can share the same name and hence framework can provide implicit mapping instead of explicit mapping through configurations. Though it may result in little loss of flexibility in extreme cases but will work with all applications following the convention.
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Ans. Yes, It may result in some loss of flexibility as the application has to follow all conventions. Moreover it can contradict with other design paradigms or principles used in the application or framework.
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Ans. Convention over configuration is a way of software design used by frameworks that attempt to decrease the number of decisions that a developer is required to make without necessarily losing flexibility. The objective is to reduce the unnecessary configurations and follow conventions to accomplish that. For example - DB Entity and DB Table name conventionally should be same and hence shouldn't require configuring mapping between the two.
"Spring Boot" and "Ruby on Rails" have adopted this design principle.
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