Mastering Java Interfaces and Strings

What is an interface in Java?

• An interface can contain implementation of methods.

• An interface is a way to create objects in Java.

• An interface in Java is a contract that classes can implement, defining methods that must be created in the implementing class.

• An interface is a type of class in Java.

How do you declare an interface in Java?

• interface MyInterface { void myMethod(); }

• public class MyInterface { void myMethod(); }

• MyInterface interface { void myMethod(); }

• public interface MyInterface { void myMethod(); }

What is the purpose of the 'implements' keyword?

• To define a new class

• To create a variable

• To indicate that a class implements an interface.

• To inherit properties from another class

Explain the difference between an abstract class and an interface.

• An abstract class can have implemented methods and state, while an interface only defines method signatures and cannot hold state.

• An abstract class can only be instantiated, while an interface cannot be instantiated at all.

• An abstract class can have multiple inheritance, while an interface cannot have any inheritance.

• An abstract class cannot have any methods, while an interface can have implemented methods.

Which method is used to compare two strings for equality in Java?

• compareTo()

• stringCompare()

• isEqual()

• equals()

What is the output of '"Hello".length()' in Java?

• 5

• Hello World

• 4

• 6

How do you convert a string to lowercase in Java?

• myString.convertToLower()

• myString.toLower()

• myString.lowercase()

• myString.toLowerCase()

What is the difference between StringBuilder and StringBuffer?

• StringBuilder is faster and not thread-safe; StringBuffer is thread-safe but slower.

• StringBuilder is immutable while StringBuffer is mutable.

• StringBuilder and StringBuffer are identical in performance and thread safety.

• StringBuilder is slower and thread-safe; StringBuffer is faster and not thread-safe.

How do you create a custom package in Java?

• Create a package without a directory structure.

• Create a directory structure, declare the package in your Java files, and compile them.

• Use only one Java file for the package.

• Compile without declaring the package name.

What is the default access modifier for classes in a package?

• protected

• public

• private

• package-private