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Questions and Answers
What are parameters?
What are parameters?
What is the method signature?
What is the method signature?
The name of the method and parameter list.
What is Javadoc?
What is Javadoc?
A specific standard for commenting Java programs.
Strings in Java are mutable.
Strings in Java are mutable.
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Which of the following is a compile time error?
Which of the following is a compile time error?
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What will happen if you call a method on a null object?
What will happen if you call a method on a null object?
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What is method overloading?
What is method overloading?
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What does 'this' keyword refer to?
What does 'this' keyword refer to?
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Match the following error types with their descriptions:
Match the following error types with their descriptions:
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What happens when primitives are passed as parameters?
What happens when primitives are passed as parameters?
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What is the purpose of a constructor?
What is the purpose of a constructor?
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What is a class variable?
What is a class variable?
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How do you create an Array in Java?
How do you create an Array in Java?
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Study Notes
Parameters and Method Calls
- Parameters act as inputs for methods, allowing data to be passed in.
- Method calls follow the syntax: methodName(parameter, parameter);.
- The style of invoking a method can involve user input, illustrated by echoing a string with parameters.
Method Return Types
- The method return type indicates what type of value will be returned (e.g., int, double, String, or void).
- For methods without a return value, use void, while return types determine the data type of the return value.
Method Signature and Javadoc
- A method signature includes the name and parameter list, such as
private int square(int x);. - Javadoc is a standardized commenting method for Java programs, starting with a comment format before the method declaration.
String Properties and Manipulations
- Strings are objects representing sequences of characters, indexed starting from 0 and are immutable (unchangeable).
- Use the ‘+’ operator to concatenate strings, forming new strings in the process.
Error Types and Common Exceptions
- Compile Time Errors occur during compilation due to syntax issues, while Run Time Errors appear during program execution, such as division by zero.
- Common exceptions include ArithmeticException, IndexOutOfBoundsException, and NullPointerException, each indicating specific programming errors.
Object-Oriented Concepts
- Objects contain state (data) and behavior (methods) and are instances of classes.
- Classes serve as templates for creating objects, defining their common behaviors and properties.
- Instance variables hold the state for each object, with each instance of a class having its unique data attributes.
Constructors and Methods
- Constructors initialize objects and set instance variable values, specified with matching parameters.
- Instance methods define the behavior of objects and can access instance variables.
Accessor and Modifier Methods
- Getter methods allow access to instance variables, while Setter methods modify their values, following naming conventions for clarity.
Static Class Components
- Static variables and methods belong to the class as a whole rather than to instances, allowing shared access without creating objects.
Method Overloading and Variable Scope
- Method overloading allows multiple methods to share the same name but requires differing parameter types, numbers, or orders.
- Variable scope defines the visibility of variables, existing from their declaration until the end of the block.
Java Packages and Visibility
- Packages group related classes, and can be imported either entirely or selectively.
- Visibility modifiers control access: Public allows access anywhere, and Private restricts it to within the defining class.
The this Keyword and Object References
- The
thiskeyword refers to the current object, resolving naming conflicts and clarifying instance variable references. - Objects in memory are referenced by pointers, requiring methods like
.equals()for value comparison instead of==which compares memory locations.
Primitives and Objects as Parameters
- Passing primitives to methods copies their data, leaving the original unchanged.
- Passing objects allows changes to the parameter to affect the original object due to shared references.
NullPointerException and Abstract Classes
- A NullPointerException arises when methods are invoked on uninitialized object references.
- Abstract classes cannot be instantiated and may contain abstract methods that subclasses must implement.
Data Structures in Java
- Common data structures include Arrays, ArrayLists, and HashMaps, each organizing data in unique ways.
- Arrays hold fixed numbers of elements of the same type, and ArrayLists automatically resize, offering additional methods for manipulation.
Working with Arrays
- Arrays are created through the syntax
Type[] arrayName = new Type[numElements];and support accessing and modifying values via indices. - Use
arrayName.lengthto retrieve the total number of elements, with iteration achieved through loops.
ArrayList Functionality
- ArrayLists can dynamically resize and easily manipulate elements, making them versatile for handling collections.
Studying That Suits You
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Description
Test your understanding of key concepts in AP Computer Science A with these flashcards. Cover essential topics such as parameters, method calls, and return types. Perfect for quick reviews and exam preparation.
