Defining Classes II - Java - page 289

Display 5.18 Use of the Method Double.parseDouble (part 1 of 2)

27 double number1 = Double.parseDouble(string1);

28 double number2 = Double.parseDouble(string2);

29 System.out.print("You input ");

30 System.out.println(number1 + " and " + number2);

31 }

32 }

Sample Dialogue
Enter two numbers on a line.
Place a comma between the numbers.
Extra blank space is OK.
41.98, 42
You input is 41.98 and 42.0

Self-Test Exercises
32. What is wrong with a program that starts as follows? The class ToyClass is
defined in Display 5.11.

ToyClass anObject = null ;
anObject.set("Josephine", 42);

33. What is the type of the constant null ?
34. Suppose aVariable is a variable of a class type. Which of the following correctly
tests to see whether aVariable contains null ?

aVariable.equals( null )
aVariable == null

35. Is the following legal in Java? The class ToyClass is defined in Display 5.11.

System.out.println( new ToyClass("Mr. Cellophane", 0));

TIP: Use Static Imports ★

You have already seen import statements, such as the following from Display 5.9:

import java.util.Scanner;

There is another form of import statement which, while not essential, can be a conven-
ience. These are called static import statements and are best explained with an example.

static import
statement

(continued)