8:00 Quiz 3

Statistics:

mean     19.476 (818.000/42)
stddev   4.495
median   20.000
midrange 16.000-22.000

#  avg
1  5.21 / 10
2  4.19 / 5
3 10.07 / 15

Question 3-1

What distinguishes the purpose of a class method from an instance method? That is, how should you decide whether a particular behavior should be an instance method or a class method? (I am not asking how they are syntactically distinguished in Java. The syntactic distinction is that a class method includes a static keyword in its declaration, while an instance method does not.)

Question 3-2

Name Java's seven primitive types other than boolean. For each, specify whether the type requires 8 bits, 16 bits, 32 bits, or 64 bits.

Question 3-3

Define a Counter class to represent simple counting devices. It should include the following methods.

Counter(): (Constructor method) Constructs a counter holding the initial value 0.
void increment(): Adds one to the value represented by the counter.
int getValue(): Returns the current value represented by the counter.

The following run() method illustrates the use of the Counter type you are to define.

public static void run() {
    Counter a = new Counter();
    Counter b = new Counter();
    a.increment();
    IO.println(a.getValue());     // prints ``1''
    a.increment();
    b.increment();
    IO.println(a.getValue());     // prints ``2''
    IO.println(b.getValue());     // prints ``1''
}

Write your answer below.

public class Counter {

    // : (your code here)

}

Solutions

Solution 3-1

An instance method is a behavior that applies to specific objects of a class, while a class method is a behavior that applies to the class as a whole. When you call an instance method, you must apply it to a particular object (e.g., file.readInt(), where file is an InputFile object); but a class method can be applied to the entire class (e.g., IO.readInt(), which uses the readInt() class method in the IO class).

Solution 3-2

`byte`	8
`short`	16
`int`	32
`long`	64
`float`	32
`double`	64
`char`	16

Solution 3-3

public class Counter {
    private int val;

    public Counter() {
        val = 0;
    }

    public void increment() {
        val++;
    }

    public int getValue() {
        return val;
    }
}