Let's discuss about most important java interview questions : 1) Explain about oops concepts? 2)Explain about memory management i.e. JVM ? 3) What are various modifiers in java ? 4) What is string in java ? Why this is immutable ? 5)What is difference between synchronized block or synchronized method ? 6)How one thread can take two object lock? 7)When we call wait method which class method is called .How its realses lock ? 8)What will happen if class is mutable and used as key in hashmap ? 9)why we create setter getter in pojo classes? 10)How will you design a class to use that class as key in hashmap ? 11)What is memory leak and write a program for memory leak ? 12)explain Hash code and equals method in detail? 13)How hash map work or explain hash map internal working ?