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Ans. Declaration is intimation to the compiler about the nature of Data a reference is going to hold.
For example - List myList;
Instantiation is reservation of memory.
For example
myList = new ArrayList();
Initialization or construction is setting the default values for member elements.
For example
myList = new ArrayList(mySet);
** Example 2nd is both for instantiation as well as initialization. The only difference is that 2nd will initialized the member elements to their default values whereas 3rd will initialized it with the elements from set.
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LikeDiscussCorrect / Improve  declaration   instantiation   initialization   construction   declaration vs instantiation   instantiation vs initialization   declaration vs initialization Asked in 1 Companiesbasic  frequent
Frequently asked question in companies using Hibernate.
Ans. It's a feature to lazily initialize dependencies , relationship and associations from the Database. Any related references marked as @OneToMany or @ManyToMany are loaded lazily i.e when they are accessed and not when the parent is loaded.
Ans. Yes, we can do that. Compiler wont complain. But using object reference we can only access methods which have been defined for object class i.e clone(), equals(), hashCode(), toString() etc.
We cannot access methods defined in String class or in any class in hierarchy between String and Object.
For example - we cannot do obj.append("abc") as it will now give compile time error.
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Ans. Constructor has the same name as class name whereas instance initialization block just have a body without any name or visibility type.
instance initialization blocks are useful if we want to have some code run regardless of which constructor is used or if we want to do some instance initialization for anonymous classes.
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Ans. Lazy Initialization means , Load Dependencies when required. Which means less load on application resources as only required data is loaded upfront. It's not only good for better performance but for better resource utilization too.
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Ans. The error states that Hibernate is not able to initialize proxy / dependent entity objects as there is no session or transaction present. Very likely we are trying to load the dependent entities lazily but the call to dependent object property is not wrapped within the session or transaction.
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Q14. If you are given choice to avoid LazyInitializationException using any of the following measures, which are the ones you will choose and why ?
1. Set lazy=false in the hibernate config file.
2. Set @Basic(fetch=FetchType.EAGER) at the mapping.
3. Make sure that we are accessing the dependent objects before closing the session.
4. Force initialization using Hibernate.initialize