prog patterns

8/6/2019 Prog Patterns

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Mehran Sahami Handout #11

CS 106A October 5, 2007

Simple Programming PatternsBased on a handout by Eric Roberts

This handout summarizes some of the most common programming patterns that you will

encounter in Java. Each of these patterns is covered in more detail in Chapters 2, 3, or 4of the textbook, but it's good to have them in a simple handy reference as well.

The first set of patterns involves getting data in and out of the computer, which provide

the necessary support for the input and output phases of a typical programming task. The

patterns you use depend on the type of value, as shown in the following table:

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The following patterns are useful in calculations:

(QJOLVK -DYDORQJIRUP -DYDVKRUWKDQGIRUPAdd \ to [. [[\ [\

Subtract \ from[. [[\ [\Add 1 to [ (increment [). [[ [

Subtract 1 from[ (decrement [). [[ [The most helpful patterns, however, encompass programming operations on a larger scale

and help you establish the overall strategy of a program. The most important ones aredescribed in the next few sections.

7KHUHSHDW1WLPHVSDWWHUQ(page 101)This pattern is the same as it was in Karel and is used for the same purpose.

IRULQWLL1L^VWDWHPHQWVWREHUHSHDWHG

`In Java, however, you are allowed to use the value of the index variable L in the body of

the loop.

7KHUHDGXQWLOVHQWLQHOSDWWHUQ(page 102)This pattern is useful whenever you need to read in values until the user enters a

particular value to signal the end of input. Such values are called VHQWLQHOV.

ZKLOHWUXH^SURPSWXVHUDQGUHDGLQDYDOXHLIYDOXHVHQWLQHOEUHDNUHVWRIERG\

`

http://technicalsupportindia.blogspot.com/


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Mehran Sahami Handout #12

CS 106A October 5, 2007

Assignment #2: Simple Java Programs

Due: 3:15pm on Monday, October 15thBased on a handout by Eric Roberts

Your job in this assignment is to write programs to solve each of these six problems.

1. Write a GraphicsProgramsubclass that draws a pyramid consisting of bricks

arranged in horizontal rows, so that the number of bricks in each row decreases by

one as you move up the pyramid, as shown in the following sample run:

The pyramid should be centered at the bottom of the window and should use

constants for the following parameters:

BRICK_WIDTH The width of each brick (30 pixels)

BRICK_HEIGHT The height of each brick (12 pixels)

BRICKS_IN_BASE The number of bricks in the base (14)

The numbers in parentheses show the values for this diagram, but you must be ableto change those values in your program.



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2.

archery target or, if you prefer commercial applications, a logo for a national

department store chain that looks like this:

This figure is simply three GOval objects, two red and one white, drawn in the correct

order. The outer circle should have a radius of one inch (72 pixels), the white circle

has a radius of 0.65 inches, and the inner red circle has a radius of 0.3 inches. The

figure should be centered in the window of a GraphicsProgramsubclass.

3. Write a GraphicsProgramsubclass that draws a partial diagram of the acm.program

class hierarchy, as follows:

The only classes you need to create this picture are GRect, GLabel, and GLine. The

major part of the problem is specifying the coordinates so that the different elements



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of the picture are aligned properly. The aspects of the alignment for which you are

responsible are:

The ZLGWK and KHLJKW of the class boxes should be specified as named constants

so that they are easy to change.

The labels should be centered in their boxes. You can find the width of a label by

calling label.getWidth() and the height it extends above the baseline by calling

label.getAscent(). If you want to center a label, you need to shift its origin by

half of these distances in each direction.

The connecting lines should start and end at the center of the appropriate edge of

the box.

The entire figure should be centered in the window.

4. In high-school geometry, you learned the Pythagorean theorem for the relationship ofthe lengths of the three sides of a right triangle:

D2 + E2 = F2

which can alternatively be written as:

F = ba22

Most of this expression contains simple operators covered in Chapter 3. The one

functionMath.sqrt. For example, the statement

double y = Math.sqrt(x);sets y to the square root ofx.

Write a ConsoleProgramthat accepts values fora andb as ints and then calculates

the solution of c as a double. Your program should be able to duplicate the

following sample run:



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5. Write a ConsoleProgramthat reads in a list of integers, one per line, until a sentinel

value of 0 (which you should be able to change easily to some other value). When the

sentinel is read, your program should display the smallest and largest values in the

list, as illustrated in this sample run:

Your program should handle the following special cases:

If the user enters only one value before the sentinel, the program should report

that value as both the largest and smallest.

If the user enters the sentinel on the very first input line, then no values have been

entered, and your program should display a message to that effect.

6. -prize-winning book *|GHO (VFKHU %DFK contains

many interesting mathematical puzzles, many of which can be expressed in the form

of computer programs. In Chapter XII, Hofstadter mentions a wonderful problem that

is well within the scope of the control statements from Chapter 4. The problem can

be expressed as follows:

Pick some positive integer and call it Q.

IfQ is even, divide it by two.

IfQ is odd, multiply it by three and add one.

Continue this process until Q is equal to one.

On page 401 of the Vintage edition, Hofstadter illustrates this process with the

following example, starting with the number 15:

15 is odd, so I make 3Q+1: 4646 is even, so I take half: 2323 is odd, so I make 3Q+1: 7070 is even, so I take half: 3535 is odd, so I make 3Q+1: 106

106 is even, so I take half: 5353 is odd, so I make 3Q+1: 160



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160 is even, so I take half: 8080 is even, so I take half: 4040 is even, so I take half: 2020 is even, so I take half: 1010 is even, so I take half: 5

5 is odd, so I make 3Q+1: 1616 is even, so I take half: 88 is even, so I take half: 44 is even, so I take half: 22 is even, so I take half: 1

As you can see from this example, the numbers go up and down, but eventually at

least for all numbers that have ever been tried comes down to end in 1. In some

respects, this process is reminiscent of the formation of hailstones, which get carried

upward by the winds over and over again before they finally descend to the ground.

Because of this analogy, this sequence of numbers is usually called the +DLOVWRQHVHTXHQFH although it goes by many other names as well.

Write a ConsoleProgramthat reads in a number from the user and then displays the

showing the number of steps taken to reach 1. For example, your program should be

able to produce a sample run that looks like this:

The fascinating thing about this problem is that no one has yet been able to prove that

it always stops. The number of steps in the process can certainly get very large. How

many steps, for example, does your program take when Q is 27?


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