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Java Basics

1/25 Which interface in Java is used for sorting and ordering?
- List
- Set
- Comparable
- Comparator
2/25 Which of the following is true about a 'final' class in Java?
- It can be extended by other classes
- It cannot be instantiated
- It can have final methods only
- It cannot be extended by other classes
3/25 What is the significance of the 'main' method in a Java application?
- It's the method that runs when a class is instantiated
- It's used to define variables
- It's the entry point of a Java application
- It's used to clean up resources before exiting the application
4/25 What is the function of the 'extends' keyword in Java?
- To inherit methods from an interface
- To extend a method's functionality
- To inherit properties and methods from a superclass
- To extend the memory allocation for an object
5/25 In Java, what is the difference between '==' and 'equals()'?
- '==' checks for value equality, 'equals()' checks for reference equality
- '==' checks for reference equality, 'equals()' checks for value equality
- There is no difference
- 'equals()' is used only for strings
6/25 What does the 'abstract' keyword signify in a Java class?
- The class can't be instantiated directly
- The class is fully implemented
- The class is optimized for performance
- The class can be instantiated multiple times
7/25 How do you declare a constant variable in Java?
- Using the 'constant' keyword
- Using the 'static final' keywords
- Using the 'immutable' keyword
- Declaring without initialization
8/25 In Java, what is the purpose of the Collections.sort() method?
- To sort elements of a collection in descending order
- To randomly shuffle elements of a collection
- To sort elements of a collection in ascending order
- To reverse the order of elements in a collection
9/25 Which of the following is a checked exception in Java?
- NullPointerException
- ArrayIndexOutOfBoundsException
- IOException
- RuntimeException
10/25 Which collection interface represents a key-value pair in Java?
- List
- Set
- Map
- Queue
11/25 What does the 'synchronized' keyword ensure in a multi-threaded environment?
- Faster execution of threads
- That only a single thread can access the method or block at a time
- That multiple threads can execute the method concurrently
- That the method will always be executed by the main thread
12/25 What is the primary difference between 'StringBuffer' and 'StringBuilder' in Java?
- StringBuffer is mutable, while StringBuilder is immutable
- StringBuilder is faster as it is not synchronized
- StringBuffer can store characters, while StringBuilder cannot
- StringBuilder is thread-safe, while StringBuffer is not
13/25 In Java, which method you must override to use an object as a key in a HashMap?
- hashKey()
- mapKey()
- equals() and hashCode()
- getKey()
14/25 How do you create a thread-safe singleton in Java?
- Using double-checked locking
- By making all methods synchronized
- By declaring all variables as volatile
- By using a static class
15/25 What is the difference between 'static' and 'non-static' methods in Java?
- Static methods can be called without creating an instance of the class
- Non-static methods are always synchronized
- Static methods are faster
- Non-static methods can access any class variable
16/25 In Java, what is 'reflection' used for?
- To modify the behavior of a program at runtime
- To duplicate objects
- To analyze the performance of applications
- To convert primitive types into objects
17/25 Which method in the Object class is used to obtain a unique hash code for the object?
- uniqueCode()
- hashCode()
- identityHashCode()
- getObjectHash()
18/25 How can you achieve thread safety in Java?
- By using synchronized blocks or methods
- By avoiding the use of multiple threads
- By using the 'volatile' keyword
- By making all methods and variables private
19/25 In Java, what does the 'transient' keyword do when applied to a class field?
- Makes the field non-serializable
- Marks the field as temporary and not part of the class's persistent state
- Indicates that the field value can change rapidly
- Makes the field volatile
20/25 What is the use of the 'implements' keyword in Java?
- To inherit from an abstract class
- To include an interface in a class
- To mark a method as mandatory to override
- To declare a class as abstract
21/25 In Java, what is the function of the 'super' keyword?
- To call a method of the superclass
- To declare superior variables
- To access the superclass's static methods
- To create an object of the superclass
22/25 What is 'polymorphism' in the context of Java?
- The ability of a variable to hold objects of different types
- The ability of Java to run on different platforms without modification
- The ability of a method to perform different tasks based on the object
- Changing the behavior of an object at runtime
23/25 In Java, which method would you use to compare two String objects for content equality?
- compareTo()
- equals()
- match()
- equalContent()
24/25 In Java, what is the default value of a boolean variable in a class?
- true
- false
- null
- 0
25/25 What does the 'static' keyword signify when applied to a block of code in Java?
- The code block is related to the static members of the class
- The code block cannot be modified
- The code block is executed when the JVM loads the class
- The code block is executed immediately after the class is instantiated
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