OBJECT-ORIENTED THINKING - Introduction to Java Programming: Comprehensive Version - page 383

10.7

✓ ✓

Describe primitive-type wrapper classes.

Check

10.8

Can each of the following statements be compiled?

Point

a. Integer i = new Integer( "23" );
b. Integer i = new Integer( 23 );
c. Integer i = Integer.valueOf( "23" );
d. Integer i = Integer.parseInt( "23" , 8 );
e. Double d = new Double();
f. Double d = Double.valueOf( "23.45" );
g. int i = (Integer.valueOf( "23" )).intValue();
h. double d = (Double.valueOf( "23.4" )).doubleValue();
i. int i = (Double.valueOf( "23.4" )).intValue();
j. String s = (Double.valueOf( "23.4" )).toString();
10.9 How do you convert an integer into a string? How do you convert a numeric string
into an integer? How do you convert a double number into a string? How do you
convert a numeric string into a double value?
10.10 Show the output of the following code.

public class Test {
public static void main(String[] args) {
Integer x = new Integer( 3 );
System.out.println(x.intValue());
System.out.println(x.compareTo( new Integer( 4 )));
}
}

10.11

What is the output of the following code?

public class Test {
public static void main(String[] args) {
System.out.println(Integer.parseInt( "10" ));
System.out.println(Integer.parseInt( "10" , 10 ));
System.out.println(Integer.parseInt( "10" , 16 ));
System.out.println(Integer.parseInt( "11" ));
System.out.println(Integer.parseInt( "11" , 10 ));
System.out.println(Integer.parseInt( "11" , 16 ));
}
}

10.8 Automatic Conversion between Primitive Types
and Wrapper Class Types
A primitive type value can be automatically converted to an object using a wrapper
class, and vice versa, depending on the context.

Key
Point

Converting a primitive value to a wrapper object is called boxing . The reverse conversion is
called unboxing . Java allows primitive types and wrapper classes to be converted automati-
cally. The compiler will automatically box a primitive value that appears in a context requir-
ing an object, and will unbox an object that appears in a context requiring a primitive value.
This is called autoboxing and autounboxing .

boxing
unboxing

autoboxing
autounboxing