AP Computer Science a Flashcards: Constructors

What this deck covers

This deck focuses on Constructors, giving you a quick way to review the definitions, rules, and examples that matter most for AP Computer Science a.

How to use these flashcards

Work through these flashcards in short sessions. Try to answer each prompt before flipping the card, then revisit any cards you miss until the explanation feels automatic.

Flashcard 1: When is the default constructor provided?

Answer: When no other constructors are defined. Java removes default constructor once any constructor is explicitly created.

Flashcard 2: Find the issue: class C { C(int x) { this.x = x; } }

Answer: No default constructor; must provide 'x'. Default constructor is removed when parameterized constructor exists.

Flashcard 3: When is the default constructor provided?

Answer: When no other constructors are defined. Java removes default constructor once any constructor is explicitly created.

Flashcard 4: Which constructor is invoked first in inheritance?

Answer: The parent class's constructor. Inheritance follows bottom-up constructor execution order.

Flashcard 5: How are static fields initialized in constructors?

Answer: Static fields are not initialized in constructors. Static fields belong to class, initialized once at class loading.

Flashcard 6: Find the issue: class F { F() { super(); } }

Answer: No issue if superclass has a default constructor. Explicit super() call is redundant but valid.

Flashcard 7: What happens if 'super()' is not explicitly called?

Answer: Java calls it automatically if not specified. Java inserts super() automatically if not explicitly written.

Flashcard 8: Find the error: class I { I(String str) {} I() { this(str); } }

Answer: 'str' is not accessible in 'I()'. Local parameter 'str' from other constructor is not accessible.

Flashcard 9: Identify the visibility modifier typically used for constructors.

Answer: public. Allows objects to be created from outside the class.

Flashcard 10: How is constructor inheritance handled in Java?

Answer: Constructors are not inherited in Java. Child classes must define their own constructors explicitly.

Flashcard 11: What is the syntax to call a constructor within another constructor?

Answer: Use 'this()' with appropriate parameters. Must be the first statement and match parameter types.

Flashcard 12: What is constructor delegation?

Answer: Using one constructor to call another in the same class. Reduces code duplication by calling other constructors.

Flashcard 13: What is constructor overloading?

Answer: Multiple constructors with different parameters. Provides flexibility for different initialization scenarios.

Flashcard 14: What does 'this()' aim to resolve?

Answer: Constructor chaining within the same class. Enables code reuse between constructors in same class.

Flashcard 15: How does the JVM handle constructor absence?

Answer: Provides a no-argument constructor by default. Only when no constructors are explicitly defined by programmer.

Flashcard 16: Which keyword is used to invoke a constructor?

Answer: new. Creates a new object instance and calls the appropriate constructor.

Flashcard 17: Identify the issue: class J { J(int k) {} J(double k) {} }

Answer: No issue; this is constructor overloading. Different parameter types allow valid constructor overloading.

Flashcard 18: How does constructor chaining work?

Answer: Using 'this()' to call another constructor in the same class. Must be the first statement in the constructor body.

Flashcard 19: What is a constructor in Java?

Answer: A special method to initialize objects. Called automatically when an object is created with 'new'.

Flashcard 20: Which keyword is used to invoke a constructor?

Answer: new. Creates a new object instance and calls the appropriate constructor.

Flashcard 21: Identify the error: class A { A() {} void A() {} }

Answer: Method 'void A()' cannot be a constructor. Constructors cannot have return types, including void.

Flashcard 22: What is a copy constructor?

Answer: A constructor that creates a copy of an object. Takes another object as parameter to duplicate its state.

Flashcard 23: How does constructor chaining work?

Answer: Using 'this()' to call another constructor in the same class. Must be the first statement in the constructor body.

Flashcard 24: Which constructor is invoked first in inheritance?

Answer: The parent class's constructor. Inheritance follows bottom-up constructor execution order.

Flashcard 25: Which constructor type can be implicit?

Answer: The default constructor. Java provides it automatically when no constructors exist.

Flashcard 26: When is 'super()' required in a constructor?

Answer: When the parent class has no default constructor. Must explicitly call parameterized parent constructor with super().

Flashcard 27: Identify the visibility modifier typically used for constructors.

Answer: public. Allows objects to be created from outside the class.

Flashcard 28: What is the effect of constructor overloading?

Answer: Allows different initialization scenarios. Multiple ways to create objects with different initial states.

Flashcard 29: How do you declare a constructor in Java?

Answer: Same name as the class, no return type. Must match class name exactly and cannot have void or any return type.

Flashcard 30: How are static fields initialized in constructors?

Answer: Static fields are not initialized in constructors. Static fields belong to class, initialized once at class loading.

Flashcard 31: What is a parameterized constructor?

Answer: A constructor with parameters to initialize fields. Accepts arguments to set specific initial values for fields.

Flashcard 32: What is the default constructor?

Answer: A no-argument constructor provided by Java. Automatically created by Java if no constructors are explicitly defined.

Flashcard 33: Find the issue: class C { C(int x) { this.x = x; } }

Answer: No default constructor; must provide 'x'. Default constructor is removed when parameterized constructor exists.

Flashcard 34: What is the role of 'super()' in a constructor?

Answer: To call the parent class's constructor. Ensures parent class is properly initialized before child class.

Flashcard 35: What is the effect of constructor overloading?

Answer: Allows different initialization scenarios. Multiple ways to create objects with different initial states.

Flashcard 36: Identify the problem: class G extends H { G() {} }

Answer: If H has no default constructor, error occurs. Depends on whether H has an accessible no-argument constructor.

Flashcard 37: What is a parameterized constructor?

Answer: A constructor with parameters to initialize fields. Accepts arguments to set specific initial values for fields.

Flashcard 38: Find the issue: class F { F() { super(); } }

Answer: No issue if superclass has a default constructor. Explicit super() call is redundant but valid.

Flashcard 39: Identify the issue: class J { J(int k) {} J(double k) {} }

Answer: No issue; this is constructor overloading. Different parameter types allow valid constructor overloading.

Flashcard 40: What happens if 'super()' is not explicitly called?

Answer: Java calls it automatically if not specified. Java inserts super() automatically if not explicitly written.

Flashcard 41: What is the primary function of a constructor block?

Answer: To execute code for every new object instance. Runs initialization code every time an object is instantiated.

Flashcard 42: What does 'this()' aim to resolve?

Answer: Constructor chaining within the same class. Enables code reuse between constructors in same class.

Flashcard 43: Which constructor type can be implicit?

Answer: The default constructor. Java provides it automatically when no constructors exist.

Flashcard 44: What happens if a constructor is private?

Answer: Object creation is limited to the class itself. Prevents external instantiation, used in singleton pattern.

Flashcard 45: What is the main rule of constructor execution order?

Answer: Base class constructors execute before derived class. Superclass initialization happens before subclass initialization.

Flashcard 46: Identify the problem: class G extends H { G() {} }

Answer: If H has no default constructor, error occurs. Depends on whether H has an accessible no-argument constructor.

Flashcard 47: What is constructor overloading?

Answer: Multiple constructors with different parameters. Provides flexibility for different initialization scenarios.

Flashcard 48: How does the JVM handle constructor absence?

Answer: Provides a no-argument constructor by default. Only when no constructors are explicitly defined by programmer.

Flashcard 49: What happens if a constructor is private?

Answer: Object creation is limited to the class itself. Prevents external instantiation, used in singleton pattern.

Flashcard 50: Find the error: class I { I(String str) {} I() { this(str); } }

Answer: 'str' is not accessible in 'I()'. Local parameter 'str' from other constructor is not accessible.

Flashcard 51: What is the primary function of a constructor block?

Answer: To execute code for every new object instance. Runs initialization code every time an object is instantiated.

Flashcard 52: Identify the use of the 'this' keyword in constructors.

Answer: To refer to the current object's fields. Resolves naming conflicts between parameters and instance variables.

Flashcard 53: What is constructor delegation?

Answer: Using one constructor to call another in the same class. Reduces code duplication by calling other constructors.

Flashcard 54: How is constructor inheritance handled in Java?

Answer: Constructors are not inherited in Java. Child classes must define their own constructors explicitly.

Flashcard 55: When is 'super()' required in a constructor?

Answer: When the parent class has no default constructor. Must explicitly call parameterized parent constructor with super().

Flashcard 56: What is a copy constructor?

Answer: A constructor that creates a copy of an object. Takes another object as parameter to duplicate its state.

Flashcard 57: What is the syntax to call a constructor within another constructor?

Answer: Use 'this()' with appropriate parameters. Must be the first statement and match parameter types.

Flashcard 58: Which class member is initialized using a constructor?

Answer: Instance variables. Object fields that store the state of each instance.

Flashcard 59: Identify the error: class A { A() {} void A() {} }

Answer: Method 'void A()' cannot be a constructor. Constructors cannot have return types, including void.

Flashcard 60: How do you differentiate a constructor from a method?

Answer: Constructors have no return type. Methods have return types; constructors initialize objects instead.

Flashcard 61: How do you differentiate a constructor from a method?

Answer: Constructors have no return type. Methods have return types; constructors initialize objects instead.

Flashcard 62: Identify the issue: class D { D() { this(5); } D(int y); }

Answer: Missing constructor body for 'D(int y)'. Constructor declaration lacks implementation body with braces.

Flashcard 63: What is the default constructor?

Answer: A no-argument constructor provided by Java. Automatically created by Java if no constructors are explicitly defined.

Flashcard 64: Identify the use of the 'this' keyword in constructors.

Answer: To refer to the current object's fields. Resolves naming conflicts between parameters and instance variables.

Flashcard 65: How do you declare a constructor in Java?

Answer: Same name as the class, no return type. Must match class name exactly and cannot have void or any return type.

Flashcard 66: How can constructors enforce immutability?

Answer: By initializing all fields and avoiding setters. Constructor sets final fields once, preventing later modification.

Flashcard 67: What is the role of 'super()' in a constructor?

Answer: To call the parent class's constructor. Ensures parent class is properly initialized before child class.

Flashcard 68: Identify the purpose of a constructor.

Answer: To initialize an object's fields. Sets initial values for instance variables when object is created.

Flashcard 69: How can constructors enforce immutability?

Answer: By initializing all fields and avoiding setters. Constructor sets final fields once, preventing later modification.

Flashcard 70: What is the main rule of constructor execution order?

Answer: Base class constructors execute before derived class. Superclass initialization happens before subclass initialization.

Flashcard 71: Identify the issue: class D { D() { this(5); } D(int y); }

Answer: Missing constructor body for 'D(int y)'. Constructor declaration lacks implementation body with braces.

Flashcard 72: Which class member is initialized using a constructor?

Answer: Instance variables. Object fields that store the state of each instance.