AP Computer Science a Quiz: Objects Instances Of Classes

Consider the following Java class and code; after executing it, what is the state of checking's balance?

// Bank account management example
class BankAccount {
    private String owner;
    private double balance;

    public BankAccount(String owner, double startingBalance) {
        this.owner = owner;
        balance = startingBalance;
    }

    public void deposit(double amount) {
        balance += amount;
    }

    public boolean withdraw(double amount) {
        if (amount <= balance) {
            balance -= amount;
            return true;
        }
        return false;
    }

    public double getBalance() {
        return balance;
    }
}

class Main {
    public static void main(String[] args) {
        BankAccount checking = new BankAccount("Ava", 200.0);
        BankAccount savings = new BankAccount("Ben", 500.0);

        checking.deposit(50.0);
        savings.withdraw(100.0);
        checking.withdraw(120.0);

        // (No printing here)
    }
}
```​

Consider the following Java class and code; after executing it, what is the state of acct2's balance?

class BankAccount {
    private String owner;
    private double balance;

    public BankAccount(String owner, double startingBalance) {
        this.owner = owner;
        balance = startingBalance;
    }

    public void deposit(double amount) {
        balance += amount;
    }

    public boolean withdraw(double amount) {
        if (amount <= balance) {
            balance -= amount;
            return true;
        }
        return false;
    }

    public double getBalance() {
        return balance;
    }
}

class Main {
    public static void main(String[] args) {
        BankAccount acct1 = new BankAccount("Ava", 100.0);
        BankAccount acct2 = acct1; // two references to the same object

        acct2.deposit(40.0);
        acct1.withdraw(10.0);

        System.out.println(acct2.getBalance());
    }
}
```​

public class Counter { private static int totalCount = 0; private int instanceCount;

public Counter() {
    totalCount++;
    instanceCount = 0;
}

public void increment() {
    instanceCount++;
    totalCount++;
}

public int getInstanceCount() {
    return instanceCount;
}

public static int getTotalCount() {
    return totalCount;
}

}

Consider the following code segment:

Counter c1 = new Counter(); Counter c2 = new Counter(); c1.increment(); c1.increment(); c2.increment();

After this code executes, what will c1.getInstanceCount() and Counter.getTotalCount() return?

public class Car { private String model; private int year; // constructors and methods not shown }

Based on the Car class definition, if two Car objects, car1 and car2, are created, which statement is true?

public class Student { private String name; private int studentID; // implementation not shown }

Which of the following code segments correctly declares a variable that is capable of holding a reference to a Student object?

In a zoological classification system, a Canine is a general category, while Wolf and Fox are more specific types of Canine.

If these relationships were modeled using classes in Java, which of the following statements would be most accurate?

public class Box { /* details not shown */ }

// In some other method: Box b1 = new Box(); Box b2 = new Box(); b1 = b2;

After the code segment above is executed, which statement is true?

// Line 1: public class LightBulb { ... } // Line 2: // Line 3: LightBulb deskLamp;

In the code snippet above, what does the statement on Line 3 accomplish?

If Car is a class, which statement best explains the relationship between the Car class and the concept of inheritance in Java?

Which statement best describes a class in object-oriented programming?

In the context of Java, which of the following best defines an object?

Consider a class named Robot. Which statement accurately describes the relationship between the Robot class and objects created from it?

All classes in Java are part of a class hierarchy. What does this imply about program design and functionality?

Consider a class named Playlist designed to represent a collection of songs. Which of the following is an example of an attribute that would be defined within the Playlist class?

Which of the following statements provides the most accurate analogy for the relationship between a class and an object?

In Java, what is the role of the Object class?

A class is a formal implementation of attributes and behaviors. How do these concepts relate to an object created from that class?

Consider the following Java class and code; what is the output of the following method call?

class BankAccount {
    private String owner;
    private double balance;

    public BankAccount(String owner, double startingBalance) {
        this.owner = owner;
        balance = startingBalance;
    }

    public void deposit(double amount) {
        balance += amount;
    }

    public boolean withdraw(double amount) {
        if (amount <= balance) {
            balance -= amount;
            return true;
        }
        return false;
    }

    public double getBalance() {
        return balance;
    }
}

class Main {
    public static void main(String[] args) {
        BankAccount checking = new BankAccount("Ava", 75.0);
        BankAccount savings = new BankAccount("Ben", 125.0);

        checking.withdraw(80.0);
        System.out.println(checking.getBalance());
    }
}
```​

Consider the following Java class and code; after executing it, what is the state of checking's balance?

class BankAccount {
    private String owner;
    private double balance;

    public BankAccount(String owner, double startingBalance) {
        this.owner = owner;
        balance = startingBalance;
    }

    public void deposit(double amount) {
        balance += amount;
    }

    public boolean withdraw(double amount) {
        if (amount <= balance) {
            balance -= amount;
            return true;
        }
        return false;
    }

    public void transferTo(BankAccount other, double amount) {
        if (withdraw(amount)) {
            other.deposit(amount);
        }
    }

    public double getBalance() {
        return balance;
    }
}

class Main {
    public static void main(String[] args) {
        BankAccount checking = new BankAccount("Ava", 90.0);
        BankAccount savings = new BankAccount("Ben", 10.0);

        checking.transferTo(savings, 50.0);
        checking.transferTo(savings, 60.0);
    }
}
```​

Consider the following Java class and code; what is the effect of the method call checking.deposit(savings.getBalance()) on checking?

class BankAccount {
    private String owner;
    private double balance;

    public BankAccount(String owner, double startingBalance) {
        this.owner = owner;
        balance = startingBalance;
    }

    public void deposit(double amount) {
        balance += amount;
    }

    public boolean withdraw(double amount) {
        if (amount <= balance) {
            balance -= amount;
            return true;
        }
        return false;
    }

    public double getBalance() {
        return balance;
    }
}

class Main {
    public static void main(String[] args) {
        BankAccount checking = new BankAccount("Ava", 20.0);
        BankAccount savings = new BankAccount("Ben", 80.0);

        checking.deposit(savings.getBalance());
        System.out.println(checking.getBalance());
    }
}
```​