Suppose you are writing the definition of the default constructor of class MyClass.
Which heading is correct?
Which statement correctly constructs a MyClass object called myObject?
Suppose greetings() is declared public static void in MyClass. Which call is
correct from another class?
Given public void update(int num, String title) in MyClass and an object
myObject, which call is correct?
Suppose you are writing the parameterised constructor of Employee. Which heading is
correct?
What does the compiler do when a class declares no constructor at all?
A class declares only public Student(String name). What is the result of
new Student() elsewhere?
Which statement about constructors is false?
Where must a call to this(...) appear inside a constructor?
What is the result of compiling and executing the following Java class?
package exam;
public class Question1 {
static int start = 2;
final int end;
public Question1(int i) {
i = 5;
end = i;
}
public void fly(int distance) {
System.out.print(end - start + " ");
System.out.print(distance);
}
public static void main(String... start) {
new Question1(2).fly(5);
}
}
Which line of code, inserted at // number6, causes the application to print 5?
package exam;
public class Question3 {
private int rope = 1;
protected boolean outside;
public Question3() {
// number6
outside = true;
}
public Question3(int rope) {
this.rope = outside ? rope : rope + 1;
}
public static void main(String[] bounce) {
System.out.print(new Question3().rope);
}
}
What is the result of compiling and executing the following?
package exam;
public class Question2 {
private static int yesterday = 1;
int tomorrow = 10;
public static void main(String[] hello) { // line 5
Question2 q = new Question2();
int today = 20, tomorrow = 40; // line 7
System.out.print(today + q.tomorrow + q.yesterday);
}
}
What is the output?
public class Point {
int x;
public static void main(String[] args) {
Point a = new Point();
Point b = a;
b.x = 9;
System.out.print(a.x);
}
}
Two objects created with identical field values are compared with ==. The result is:
Why does a.equals(b) return false for two distinct objects with identical data in
a class that does not override equals?
To make equals compare contents, a class must:
What is the output?
public class Acc {
private double balance;
public void deposit(double d) { balance += d; }
public double getBalance() { return balance; }
static void bonus(Acc a) { a.deposit(100); }
public static void main(String[] args) {
Acc x = new Acc();
x.deposit(50);
bonus(x);
System.out.print(x.getBalance());
}
}
What is the output if bonus is changed to { a = new Acc(); a.deposit(100); }?
If s is an instance variable (a field), what does the declaration Student s; alone
place in s?
Which of these is a valid overloaded pair of constructors?
What is the output?
public class Book {
private String title;
public Book() { this("Untitled"); }
public Book(String t) { title = t; }
public String getTitle() { return title; }
public static void main(String[] args) {
System.out.print(new Book().getTitle());
}
}
In the previous class, how many constructors does Book have?
Which statement about public void Student() inside class Student is true?
What is the output?
public class Chain {
private int v;
public Chain set(int v) { this.v = v; return this; }
public int get() { return v; }
public static void main(String[] args) {
System.out.print(new Chain().set(3).set(7).get());
}
}
What makes the chaining in the previous question possible?
What happens when a chained call such as a.getB().getName() is evaluated and
getB() returns null?
Which statement creates two independent objects?
After Student a = new Student(); a = null;, the object originally created is:
Which is stored on the heap?
What is the output?
public class Counter {
private int n;
public Counter(int n) { this.n = n; }
public void inc() { n++; }
public int get() { return n; }
public static void main(String[] args) {
Counter a = new Counter(5);
Counter b = new Counter(5);
a.inc();
System.out.print(a.get() + " " + b.get() + " " + (a == b));
}
}
A constructor that takes no parameters and is written by the programmer is called:
Which of these is not a good reason to write several constructors for one class?
Given public Employee(String name, double salary) in Employee, which call
compiles?
Draw the memory picture (stack and heap) after these three lines and say how many objects exist.
Student a = new Student("Ali", 60);
Student b = new Student("Ali", 60);
Student c = a;
Explain the difference between a == b and a.equals(b),
and state precisely what a class must do so that the second one reports equal contents.
A student adds public Rectangle(double w, double h) to a class
and the program suddenly fails to compile at a line new Rectangle() that worked yesterday.
Explain what happened and give two ways to fix it.
Write a class Rectangle with private width and
height; a no-argument constructor that sets both to 1; a parameterised constructor that
delegates the validation to a private helper (negative values become 1); accessors, mutators,
getArea(), getPerimeter(); a boolean isSquare(); and an overridden equals
that treats two rectangles with the same dimensions as equal. Write a driver that demonstrates
every one of these, including the difference between == and equals.