Tag Archives: core java interview question

Overview of Class file Structure in Java? 1. Magic Number The first four bytes of the class file is the magic number. This is a predefined value used by JVM to identify a .class file is generated by the valid compiler or not. The value should be “OXCAFEBABE”. Note:- Whenever we are executing a java class if JVM unable to ...

What is Arrays class in Java? Arrays class is a utility class to define several utility methods for array objects.  We can sort primitive arrays only based on default natural sorting order whereas we can sort object arrays either based on default natural sorting order or based on customized sorting order Sorting elements of the array  1 Public static void ...

What is a Collection class in Java? Collections class defines several utility methods for collection objects like sorting, searching, reversing, etc.  Sorting elements of List  Collections class defines the following two methods for sorting. 1 Public static void sort(List l) To sort based on default natural sorting order In this case list should compulsory contain homogenous and comparable objects otherwise ...

What is Hashtable in Java with Example? What is Hashtable in Java with Example? The underlying data-structure for Hashtable is Hashtable. Insertion order is not preserved and it is based on Hashcode of keys. Duplicate keys are not allowed and values can be duplicated. Heterogeneous objects are allowed for both keys and values. Null is not allowed for both key and ...

  What is TreeMap in Java with example? The underlying data-structure is Red-black-Tree. Insertion order is not preserved and it is based on some sorting order of keys. Duplicate key is not allowed but values can be duplicated. If we are depending on default natural sorting order then keys should be heterogeneous and comparable. Otherwise, we will get Runtime exception saying ...

  What is WeakHashMap in Java? It is exactly same as HashMap except for the following difference:- In the case of HashMap even though object doesn’t have any reference it is not eligible for GC. If it is associated with HashMap that is HashMap dominates Garbage collector. But in the case of WeakHashMap, if the object doesn’t contain any references ...