INTRODUCTION TO OBJECTS AND INPUT/OUTPUT - Java Programming: From Problem Analysis to Program Design - page 167

Double.parseDouble(strExpression)

where strExpression is an expression containing a numeric string.
21 . The method showInputDialog of the class JOptionPane is used to
create an input dialog box.
22 . The method showMessageDialog of the class JOptionPane is used to
create an output message dialog box.
23 . The class JOptionPane is contained in the package javax.swing .
24 . If a program uses input and output dialog boxes, it must also use the statement:
System.exit(0);
25 . To format a floating-point number to a specific number of decimal places,
you can use the String method format .
26 . To input data from a file, you use the class es Scanner and FileReader ;
to send output to a file, you use the class PrintWriter .

3

27 .

File I/O is a four-step process: (i) import the necessary classes from the
package s java.util and java.io into the program; (ii) create and
associate the appropriate objects with the input/output sources; (iii) use
the appropriate methods associated with the objects created in Step ii to
input/output the data; and (iv) close the file(s).

EXERCISES

1. Mark the following statements as true or false.
a. A variable declared using a class is called an object.
b. In the statement x ¼ console.nextInt() ; , x must be a variable.
c. You generate the newline character by pressing Enter (return) on the
keyboard.
d. The methods printf and format are used to format a decimal number
to a specific number of decimal places.
2. How does a variable of a primitive type differ from a reference variable?
3. What is an object?
4. What does the operator new do?
5. Suppose that str is a String variable. Write a Java statement that uses the
operator new to instantiate the object str and assign the string "Java
Programming" to str .
6. What is garbage collection? Write the statement that instructs the Java
system to (immediately) perform garbage collection.
7. Which package contains class String ? If a program uses this class, explain
why it is not necessary to explicitly import this class using the import statement.