Laboratory: Polymorphism in Java
a. Scan through MathUtils.java and verify that
the square root method has the form described in the reading.
b. Run the main method of MathExpt to see
that it behaves as expected.
c. Extend the main method of MathExpt so that
it computes the square root of
an Integer,
a Float,
a Double,
a BigInteger,
a BigDecimal, and
a double.
As a first step in understanding the layout methods, extend the
main method of TBExpt.java so that it
uses TBUtils.print to print a simple block. I
would suggest something like the following.
TextBlock block = new TextLine("This is a test.");
TBUtils.print(pen,block);
The reading,
claims that it is possible to combine text blocks together by
using one as a parameter to the constructor of another. (In fact,
that seems to be the only way to create a BoxedBlock.
Try creating and printing out each of the following:
-
a boxed line (of your choice);
-
a boxed boxed line (of your choice); and
-
a boxed empty line.
Exercise 4: Composing Text
The classes HCompose and VCompose permit you
to compose pairs of text blocks horizontally and vertically. For
example, new HCompose(tb1,tb2) makes a text block by
putting tb1 and tb2 side-by-side, and
new VCompose(tb1,tb2) makes a text block by putting
tb1 on top of tb2.
a. Using VCompose, TextLine, and
BoxedBlock, build the following text block:
+-------+
|Hello |
|Goodbye|
+-------+
b. Using VCompose, TextLine, and
BoxedBlock, build the following text block:
+-----+
|Hello|
+-----+
+-------+
|Goodbye|
+-------+
c. Using HCompose, TextLine, and
BoxedBlock, build the following block:
+-----+Goodbye
|Hello|
+-----+
d. Using HCompose, TextLine, and
BoxedBlock, build the following block:
Goodbye+-----+
|Hello|
+-----+
Exercise 5: Writing HCompose
Assume that HCompose has two fields,
TextBlock left;
TextBlock right;
a. Sketch how you might write
String row(int rownum), int width(), and int height().
You can look at the source code of BoxedBlock for ideas,
but please do not look at the source code of HCompose.
b. Compare your answer to the source code of HCompose.
Exercise 6: Writing VCompose
Assume that VCompose has two fields,
TextBlock top;
TextBlock bottom;
a. Sketch how you might write
String row(int rownum), int width(), and
You can look at the source code of BoxedBlock and
HCompose for ideas, but please do not look at the source
code of VCompose.
b. Compare your answer to the source code of VCompose.
Exercise 7: Other Composition Classes
Pick one of the following composition mechanisms and implement it as a
class.
a. Truncate, which, given a text block and a maximum width,
builds a new block that truncates the input block to that width.
b. Center, which, given a text block and a width, builds
a new block that centers the block within that width.
c. RightJustify, which, given a text block and a width,
builds a new block right-justifies the input block within that width.
