Class Members, Utility Classes, and Program Design

How many copies of a static field exist when 50 objects of the class have been created?

What is the output?

public class Robot {
    static int built = 0;
    int serial;
    Robot() { built++; serial = built; }
    public static void main(String[] args) {
        new Robot(); new Robot();
        Robot r = new Robot();
        System.out.print(built + " " + r.serial);
    }
}

Which member can a static method use directly, with no object?

Why does the following fail to compile?

public class App {
    private int value = 5;
    public static void main(String[] args) { System.out.print(value); }
}

Which two changes would each fix the previous program?

May an instance method access a static field of the same class?

Which declaration is a correctly written class constant?

Why is main declared static?

Which of these is the best example of something that should be a static field?

Which is the best example of something that should be an instance field?

What is the output?

public class Shared {
    static int total = 0;
    int mine = 0;
    void add() { total++; mine++; }
    public static void main(String[] args) {
        Shared a = new Shared(), b = new Shared();
        a.add(); a.add(); b.add();
        System.out.print(a.mine + " " + b.mine + " " + total);
    }
}

A utility class such as Math:

Why might a utility class declare a private no-argument constructor?

Which call is correct for public static double withVat(double a) in class TaxUtil?

What is the output?

public class Bank {
    private static double rate = 0.05;
    public static void setRate(double r) { rate = r; }
    public static double getRate() { return rate; }
    public static void main(String[] args) {
        Bank a = new Bank();
        a.setRate(0.10);
        System.out.print(Bank.getRate());
    }
}

Calling a static method through an object reference (a.setRate(...) above) is:

When is a static field initialised?

What is wrong with this design?

public class Student {
    private static String name;      // every student shares one name!
    public void setName(String n) { name = n; }
}

High cohesion in a class means:

Low coupling between two classes means:

In a well-designed program, main should mostly:

A method that is 200 lines long and whose comment says “reads the file, validates the data, computes statistics and prints a report” should be:

Which javadoc tag documents what a method gives back?

Which set of test values is the best choice for a method that validates a mark between 0 and 100?

What is the output?

public class Util {
    public static int twice(int n) { return 2 * n; }
    public static int quad(int n)  { return twice(twice(n)); }
    public static void main(String[] args) { System.out.print(quad(3)); }
}

A static method calling another static method of the same class must write:

Which statement is true?

What is printed?

public class Id {
    private static int next = 100;
    private int id;
    public Id() { id = next++; }
    public int getId() { return id; }
    public static void main(String[] args) {
        Id a = new Id(), b = new Id(), c = new Id();
        System.out.print(a.getId() + " " + c.getId() + " " + next);
    }
}

Which is the correct way for one class to use a constant declared as public static final int MAX = 40; in class Config?

A program is decomposed into InputReader, StatisticsCalculator and ReportPrinter. This is an example of:

Which of the following would not be a sensible member of a utility class for string handling?

What is the output?

public class Mixed {
    static int s = 1;
    int i = 1;
    void bump() { s++; i++; }
    public static void main(String[] args) {
        Mixed m1 = new Mixed(), m2 = new Mixed();
        m1.bump(); m2.bump(); m2.bump();
        System.out.print(m1.i + "" + m2.i + s);
    }
}

Explain in your own words why a static method cannot use an instance variable directly, and describe the two ways a static method can nevertheless work with instance data.

A Library class must remember how many books have ever been borrowed across the whole system, and also how many each individual Member currently holds. Say which of these is static and which is an instance variable, and justify both choices.

Give two arguments for replacing the literal 0.19 scattered through a program with public static final double VAT = 0.19;.

Write a utility class StringUtil with static methods countVowels(String), reverse(String), isPalindrome(String) (ignoring case and spaces) and capitaliseWords(String), plus a private constructor and a short javadoc comment for each method. Write a separate driver class that tests all four with at least two inputs each, including an empty string.