JAVA

Suppose we execute the following code:

Point p, q, r, s;

p = new Point(3, 4); // create a point with x = 3, y = 4;

q = new Point(3, 4);

r = new Point(10, 20);

s = r;

q.setLocation(10, 20); // change x to 10 and y to 20

s.setLocation(3, 4);

How many of the following conditions are true? Check all that apply.

• p == q
• p == s
• q == r
• r == s
• p.getX() == 3
• q.getX() == 3
• r.getX() == 3
• s.getX() == 3

What are some things wrong with the following code?

150 String silly(Point p) {

151 String result;

152 Point last = null;

153 while (p.getX() > 0) {

154 last = p;

155 p = new Point(p.getX()-p.getY(),p.getY()+1);

156 if (p.getY() < 0) {

157 result = "Found negative";

158 p = null;

159 break;

160 }

161 }

162 return result + "last,x = " + last.getX() + ", p = " + p;

163 }

Select ALL that apply.

• Before line 153, p could be null leading to NPE
• Before line 154, last could be null, leading to NPE
• Before line 157, result could be undefined, an error
• Before line 158, p is assigned null, leading to NPE
• Before line 162, result could be undefined, an error
• Before line 162, last could be null, leading to NPE
• Before line 162, p could be null, leading to NPE

The following definition for equality on locations has problems. Which criticism is unfair or wrong?

@Override

boolean equals(Location other) {

if (x == other.x && y == other.y) {

return true;

} else {

return true;

}

}

• It should be declared public
• It should use an accessor to get x and y.
• It should take an object parameter.
• It will crash if passed null.

Which of the following actions are never performed by the default clone method?

• Throw a CloneNoSupportedException.
• Cope over all fields to the result.
• Check that the class implements Cloneable.
• Check that the method is overridden.

What is a good reason to define a static method?

• To define an operations that doesnt do anything with instances
• To define an operation that doesnt start with any instance
• To avoid modifying any variables
• For efficiency
• To declare that the method always returns the same thing.