Lecture 9 | Programming Methodology (Stanford) | Summary and Q&A

Summary

In this video, the instructor covers the topics of strings and writing your own classes in Java. He explains what strings are and how to declare and manipulate them in Java. He also introduces the concept of writing your own classes, including constructors, instance variables, and methods.

Questions & Answers

Q: What is a string in Java?

A string in Java is a type that represents a piece of text or a string of characters. It is declared using the String keyword and can be initialized with text enclosed in double quotes.

Q: How can you concatenate strings in Java?

Strings can be concatenated in Java using the + operator. This can be done when declaring a new string or when using the print or println methods.

Q: What is a class in Java and how is it different from a program?

In Java, a class is a blueprint or template for creating objects. It defines the properties and behaviors of the objects. A program, on the other hand, is a collection of classes that work together to solve a specific problem or perform a certain task.

Q: How do you declare a class in Java?

To declare a class in Java, you use the class keyword followed by the name of the class. You can also specify a superclass that the class extends, if necessary.

Q: What is a constructor in Java?

A constructor in Java is a special method that is used to initialize objects of a class. It has the same name as the class and is called automatically when an object is created. Constructors can have parameters or no parameters, depending on how the object needs to be initialized.

Q: How do you create objects of a class in Java?

To create objects of a class in Java, you use the new keyword followed by the name of the class and parentheses. This invokes the constructor of the class and returns a new instance of the class.

Q: What is the difference between a local variable and an instance variable in Java?

A local variable in Java is declared inside a method or block and its scope is limited to that method or block. An instance variable, on the other hand, is declared inside a class but outside any method or block. It is accessible to all methods of the class. Instance variables have default values if not explicitly initialized, while local variables do not.

Q: What is the difference between public and private access modifiers in Java?

In Java, the public access modifier allows a class, method, or variable to be accessed from any other class. The private access modifier restricts access to only the class where it is declared. Private members can only be accessed by other members of the same class.

Q: How are objects passed as parameters in Java?

In Java, when you pass an object as a parameter to a method, you are actually passing a reference to the object. This means that the method can modify the object and any changes made to the object inside the method will be reflected outside the method as well.

Q: What is the difference between a class variable and an instance variable in Java?

A class variable in Java is a variable that is shared by all objects of a class. There is only one copy of the variable for all objects. An instance variable, on the other hand, is unique to each object of the class. Each object has its own copy of the instance variable.