Mastering Java Interfaces and Strings

What is a Java interface and how is it used?

• A Java interface is a collection of variables that store data.

• A Java interface is a type of class that cannot be instantiated.

• A Java interface is a method that can be overridden in subclasses.

• A Java interface is a contract that classes can implement to define methods without providing their implementation.

Explain the concept of multiple inheritance in Java interfaces.

• Java interfaces can only inherit methods from their own class.

• In Java, a class can implement multiple interfaces, allowing it to inherit abstract methods from multiple sources.

• A class can only implement one interface in Java.

• Multiple inheritance is not allowed in Java interfaces.

What are the key differences between String, StringBuilder, and StringBuffer?

• String is mutable; StringBuilder is synchronized; StringBuffer is immutable.

• String is mutable; StringBuilder is immutable; StringBuffer is not synchronized.

• String is immutable; StringBuilder is mutable and not synchronized; StringBuffer is mutable and synchronized.

• String is synchronized; StringBuilder is immutable; StringBuffer is mutable.

How do you create a custom package in Java?

• Create a directory structure matching the package name and declare the package in your Java files.

• Declare the package at the end of the Java file.

• Create a package by simply naming the Java file.

• Use a single Java file to define multiple packages.

What is the purpose of the 'package' keyword in Java?

• To create a new class in Java.

• To import external libraries into a program.

• To define the main method of a Java application.

• To define a namespace for classes and organize code.

Describe how to manipulate strings using the String class methods.

• String class methods only allow for numeric operations.

• String class methods can only concatenate strings without any other functionality.

• String class methods are exclusively for formatting dates and times.

• String class methods allow for various manipulations such as accessing characters, extracting substrings, changing case, finding positions, and replacing content.

What is the difference between an abstract class and an interface?

• An abstract class can have implemented methods and state, while an interface cannot have implemented methods (except default methods) and cannot maintain state.

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

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

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

How can you implement an interface in a Java class?

• Declare the interface as a variable in the class.

• Use the 'implements' keyword in the class declaration and provide implementations for all interface methods.

• Use the 'extends' keyword in the class declaration.

• Implement only some methods of the interface.

What are the advantages of using StringBuilder over String?

• StringBuilder is more efficient for string manipulation due to its mutability, reducing memory overhead and improving performance.

• StringBuilder is less memory efficient than String.

• StringBuilder creates new strings for every modification.

• StringBuilder is slower than String for all operations.

How do you import a package in Java?

• Use the 'require' statement to include the package.

• Packages are automatically imported in Java.

• You can import a package by using the 'include' keyword.

• Use the 'import' statement followed by the package name.