Stanford CS106A - Programming Methodology (Java Basics) Flashcards

Question 1

What is Java?

Accepted Answer

Java is a high-level, object-oriented programming language known for its "write once, run anywhere" capability, achieved through the Java Virtual Machine (JVM). It's widely used for enterprise-level applications, mobile development (Android), and more.

Question 2

What is the purpose of the `main` method in a Java program?

Accepted Answer

The `main` method is the entry point for any standalone Java application. When you run a Java program, the JVM looks for and executes the `main` method first. Its signature is `public static void main(String[] args)`.

Question 3

Explain the difference between declaring and initializing a variable in Java.

Accepted Answer

1.  **Declaration:** Reserves memory for a variable and specifies its data type, e.g., `int age;`.
2.  **Initialization:** Assigns an initial value to a declared variable, e.g., `age = 30;`.
    Often, declaration and initialization are combined: `int age = 30;`.

Question 4

List and briefly describe four primitive data types in Java.

Accepted Answer

1.  `int`: Stores whole numbers (integers), e.g., `10`, `-5`.
2.  `double`: Stores floating-point numbers (decimals), e.g., `3.14`, `-0.5`.
3.  `boolean`: Stores truth values, either `true` or `false`.
4.  `char`: Stores a single character, enclosed in single quotes, e.g., `'A'`, `'7'`.

Question 5

How does the `String` data type differ from primitive data types in Java?

Accepted Answer

`String` is an object (a class), not a primitive data type. It represents a sequence of characters. Unlike primitives which store direct values, `String` variables store references to `String` objects in memory.

Question 6

What is the basic syntax for an `if` statement in Java?

Accepted Answer

An `if` statement executes a block of code only if a specified condition is `true`.
```java
if (condition) {
    // Code to execute if condition is true
}
```

Question 7

Explain the purpose and structure of an `if-else if-else` statement.

Accepted Answer

It allows for multiple conditions to be tested sequentially. The first `true` condition's block is executed, and subsequent `else if` and `else` blocks are skipped.
```java
if (condition1) {
    // Code for condition1
} else if (condition2) {
    // Code for condition2
} else {
    // Code if no conditions above are true
}
```

Question 8

When would you typically use a `for` loop in Java? Provide its basic syntax.

Accepted Answer

A `for` loop is ideal when you know exactly how many times you want to iterate, often used for iterating over arrays or a fixed range of numbers.
```java
for (initialization; condition; increment/decrement) {
    // Code to execute repeatedly
}
```

Question 9

When would you typically use a `while` loop in Java? Provide its basic syntax.

Accepted Answer

A `while` loop is used when the number of iterations is not known beforehand, and the loop continues as long as a specified condition remains `true`.
```java
while (condition) {
    // Code to execute repeatedly
    // Must include code to eventually make condition false
}
```

Question 10

What is a method (function) in Java, and why are they used?

Accepted Answer

A method is a block of code that performs a specific task. Methods promote code reusability, modularity, and make programs easier to read, debug, and maintain.

Question 11

Describe the basic structure of a method definition in Java.

Accepted Answer

```java
accessModifier static? returnType methodName(parameterType parameterName, ...) {
    // Method body
    // return value; (if returnType is not void)
}
```
Example: `public static int add(int a, int b) { return a + b; }`

Question 12

How do you call a method in Java?

Accepted Answer

To call a method, you use its name followed by parentheses containing any required arguments. If the method is part of an object, you use `objectName.methodName()`. If it's a `static` method within the same class, you can just use `methodName()`.
Example: `int sum = add(5, 3);`

Question 13

Explain the concepts of "parameters" and "arguments" in the context of methods.

Accepted Answer

1.  **Parameters:** Variables declared in the method signature that receive values when the method is called, e.g., `int a, int b` in `add(int a, int b)`.
2.  **Arguments:** The actual values passed to a method when it is invoked, e.g., `5, 3` in `add(5, 3)`.

Question 14

What is an array in Java, and how do you declare one?

Accepted Answer

An array is a data structure that stores a fixed-size sequential collection of elements of the same data type.
Declaration syntax: `dataType[] arrayName;` or `dataType arrayName[];`
Example: `int[] numbers;`

Question 15

How do you initialize an array in Java, and how do you access its elements?

Accepted Answer

1.  **Initialization:** `numbers = new int[5];` (creates an array of 5 integers, default values are 0) or `int[] numbers = {10, 20, 30};` (initializes with specific values).
2.  **Accessing elements:** Use the array name followed by the index in square brackets. Array indices are 0-based.
    Example: `int firstElement = numbers[0];`

Question 16

How do you find the number of elements in a Java array?

Accepted Answer

You use the `length` property of the array.
Example:
```java
int[] myArray = {1, 2, 3, 4, 5};
int size = myArray.length; // size will be 5
```

Question 17

What is a "class" in Java (in the context of OOP)?

Accepted Answer

A class is a blueprint or a template for creating objects. It defines the common properties (fields/attributes) and behaviors (methods) that all objects of that type will have.

Question 18

What is an "object" in Java (in the context of OOP)?

Accepted Answer

An object is an instance of a class. It's a concrete entity created from the class blueprint, possessing its own unique set of values for the properties defined by the class.

Question 19

How do you create an object from a class in Java?

Accepted Answer

You use the `new` keyword followed by the class constructor.
Example: If `Car` is a class, `Car myCar = new Car();` creates a new `Car` object named `myCar`.

Question 20

How do you access the fields (attributes) and methods of an object in Java?

Accepted Answer

You use the dot (`.`) operator.
Example: If `myCar` has a `color` field and a `start()` method:
```java
String carColor = myCar.color;
myCar.start();
```

Question 21

List three common debugging strategies in Java programming.

Accepted Answer

1.  **Print Statements:** Inserting `System.out.println()` statements to display variable values at different points in the code.
2.  **Using a Debugger:** Stepping through code line by line, setting breakpoints, and inspecting variable states using an IDE's built-in debugger.
3.  **Code Review:** Carefully reading through your code to identify logical errors or typos.

Question 22

Why are comments important in Java code, and how do you write them?

Accepted Answer

Comments explain the code's purpose, logic, or any non-obvious details, making it more understandable for others (and your future self).
*   Single-line: `// This is a single-line comment`
*   Multi-line: `/* This is a multi-line comment */`
*   Javadoc: `/** This is a Javadoc comment for documentation */`

Question 23

What are good practices for naming variables and methods in Java?

Accepted Answer

1.  **Meaningful Names:** Names should clearly indicate the variable's purpose or the method's action (e.g., `firstName`, `calculateTotal`).
2.  **CamelCase:** Start with a lowercase letter, then capitalize the first letter of each subsequent word (e.g., `myVariableName`, `computeArea`).
3.  **Avoid Abbreviations:** Unless universally understood, avoid cryptic abbreviations.
4.  **Consistency:** Stick to a consistent naming style throughout your codebase.

Stanford CS106A - Programming Methodology (Java Basics)

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