Raj questions

• Why it is necessary to override hashcode and equals method of key for Hashmap? [duplicate]
• How does Externalizable differ from Serializable? [duplicate]
• Why String class is not Cloneable?
• Scenario where extending thread is preferred than implement Runnable? [duplicate]
• why fields should be final in immutable class?
• Why LinkedList and arraylist extends AbstractList in java?

Raj answers