Classwork:
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Exercises 1 through 4 from Built-in Types of Data
A data type is a set of values and a set of operations defined on them. For example, we are familiar with numbers and with operations defined on them such as addition and multiplication. There are eight different built-in types of data in Java, mostly different kinds of numbers. We use the system type for strings of characters so frequently that we also consider it here.
Terminology. We use the following code fragment to introduce some terminology:
The first line is a declaration statement that declares the names of three variables using the identifiers a, b, and c and their type to be int. The next three lines are assignment statements that change the values of the variables, using the literals 1234 and 99, and the expression a + b, with the end result that c has the value 1333.
Characters and strings. A char is an alphanumeric character or symbol, like the ones that you type. We usually do not perform any operations on characters other than assigning values to variables. A String is a sequence of characters. The most common operation that we perform on strings is known as concatenation: given two strings, chain them together to make a new string. For example, consider the following Java program fragment:
The first statement declares three variables to be of type String. The next three statements assign values to them, with the end result that c has the value "Hello, Bob". Using string concatenation, Ruler.java prints the relative lengths of the subdivisions on a ruler.
Integers. An int is an integer (whole number) between −231 and 231 − 1 (−2,147,483,648 to 2,147,483,647). We use ints frequently not just because they occur frequently in the real world, but also they naturally arise when expressing algorithms. Standard arithmetic operators for addition, multiplication, and division, for integers are built into Java, as illustrated in IntOps.java and the following table:
Floating-point numbers. The double type is for representing floating-point numbers, e.g., for use in scientific applications. The internal representation is like scientific notation, so that we can compute with real numbers in a huge range. We can specify a floating point number using either a string of digits with a decimal point, e.g., 3.14159 for a six-digit approximation to the mathematical constant pi, or with a notation like scientific notation, e.g., 6.022E23 for Avogadro’s constant 6.022 × 1023. Standard arithmetic operators for addition, multiplication, and division, for doubles are built in to Java, as illustrated in DoubleOps.java and the following table:
Quadratic.java shows the use of doubles in computing the two roots of a quadratic equation using the quadratic formula.
Booleans. The boolean type has just two values: true or false. The apparent simplicity is deceiving—booleans lie at the foundation of computer science. The most important operators defined for the boolean are for and, or, and not.
Although these definitions are intuitive and easy to understand, it is worthwhile to fully specify each possibility for each operation in a truth table.
Comparisons. The comparison operators are mixed-type operations that take operands of one type (e.g., int or double) and produce a result of type boolean. These operations play a critical role in the process of developing more sophisticated programs.
LeapYear.java tests whether an integer corresponds to a leap year in the Gregorian calendar.
Many programming tasks involve using Java library methods in addition to the built-in operators. An application programming interface is a table summarizing the methods in a library.
You can call a method by typing its name followed by arguments, enclosed in parentheses and separated by commas. Here are some examples:
We often find ourselves converting data from one type to another using one of the following approaches.
We often find ourselves converting data from one type to another using one of the following approaches.
Solution: sets a, b, and t equal to the original value of a.
Explain each outcome.
double force = G * mass1 * mass2 / r * r;
to compute values according to the formula F = Gm1m2 / r2. Explain the problem and correct the code.
Solution: It divides by r, then multiplies by r (instead of dividing by r *r). Use parentheses:
double force = G * mass1 * mass2 / (r * r);
w = 35.74 + 0.6215 t + (0.4275 t – 35.75) v0.16
Write a program WindChill.java that takes two double command-line arguments t and v and prints the wind chill. Use Math.pow(a, b) to compute ab. Note: the formula is not valid if t is larger than 50 in absolute value or if v is larger than 120 or less than 3 (you may assume that the values you get are in that range).
y0 = y − (14 − m) / 12
x = y0 + y0/4 − y0/100 + y0/400
m0 = m + 12 × ((14 − m) / 12) − 2
d0 = (d + x + 31m0 / 12) mod 7
For example, on which day of the week was August 2, 1953?
Write a program Dragon.java to print the instructions for drawing the dragon curves of order 0 through 5. The instructions are strings of the characters F, L, and R, where F means “draw line while moving 1 unit forward”, L means “turn left”, and R means turn right. A dragon curve of order n is formed when you fold a strip of paper in half n times, then unfold to right angles. The key to solving this problem is to note that a curve of order n is a curve of order n−1 followed by an L followed by a curve of order n−1 traversed in reverse order, and then to figure out a similar description of the reverse curve.
Solution: Syntax error since <= is a binary operator. You can rewrite the expression as (90 <= grade && grade <= 100).
Solution: It prints 0.0 since the integer division is done before the cast.
Solution: The product of the two int values is computed as an int, and then automatically converted to a long. But 65536 * 65536 = 2^32 overflows a 32 bit int before it gets converted.
Solution: The compiler complains that the variable x might not have been initialized. Variables within main are not automatically initialized.
Solution: In Java, ^ does not mean exponentiation (it’s the exclusive or function from logic). Use a*a instead. To compute ax, use Math.pow(a, x). Note that Math.pow() returns a double so that you would need an explicit cast if a and b in the above example were integers.
Solution: Only the second one.
Earth-moon: m1 = 1, m2 = .0123, a = 384,000, r1 = 4,670, R1 = 6,380.
Pluto-Charon: m1 = .0021, m2 = .000254, a = 19,600, r1 = 2,110, R1 = 1,150.
Sun-Earth: m1 = 333,000, m2 = 1, a = 150,000,000, r1 = 449, R1 = 696,000.
Note that if r1 is less than the radius of the first body R1, then the barycenter lies within the first body.
P r payment = ---------------, where n = 12 * Y, r = (R / 100) / 12 1 - (1 + r)^(-n)
Caveat: in Chapter 9, we will consider more accurate ways to compute this quantity, so before you go off to run an online bank, be sure to learn about roundoff error.
Copyright © 2000–2019 Robert Sedgewick and Kevin Wayne. All rights reserved.
/******************************************************************************
* Compilation: javac Quadratic.java
* Execution: java Quadatic b c
*
* Given b and c, solves for the roots of x*x + b*x + c.
* Assumes both roots are real valued.
*
* % java Quadratic -3.0 2.0
* 2.0
* 1.0
*
* % java Quadratic -1.0 -1.0
* 1.618033988749895
* -0.6180339887498949
*
* Remark: 1.6180339... is the golden ratio.
*
* % java Quadratic 1.0 1.0
* NaN
* NaN
*
*
******************************************************************************/
public class Quadratic {
public static void main(String[] args) {
double b = Double.parseDouble(args[0]);
double c = Double.parseDouble(args[1]);
double discriminant = b*b - 4.0*c;
double sqroot = Math.sqrt(discriminant);
double root1 = (-b + sqroot) / 2.0;
double root2 = (-b - sqroot) / 2.0;
System.out.println(root1);
System.out.println(root2);
}
}
Copyright © 2000–2017, Robert Sedgewick and Kevin Wayne.
Last updated: Fri Oct 20 14:12:12 EDT 2017.
Escape Characters
Suppose you want to print a message with quotation marks in the output. Can you write a statement like this?
System.out.println(“He said “Java is fun””);
No, this statement has a compile error. The compiler thinks the second quotation character is the end of the string and does not know what to do with the rest of the characters.
To overcome this problem, Java uses a special notation to represent special characters, as shown in Table 2.6. This special notation, called an escape character, consists of a backslash (\) followed by a character or a character sequence. For example, \t is an escape character for the Tab character and an escape character such as \u03b1 is used to represent a Unicode. The symbols in an escape character are interpreted as a whole rather than individually.
So, now you can print the quoted message using the following statement:
System.out.println(“He
said \”Java is fun\””); The output is
He
said “Java is fun”
Note that the symbols \ and ” together represent one character.
Escape Characters
https://docs.oracle.com/javase/tutorial/java/data/characters.html
Do your best to approximate lines with characters, such as |, -, and +.
Write a program WindChill_YI.java that takes two double command-line arguments t and v and prints the wind chill. Use Math.pow(a, b) to compute ab.
Note: the formula is not valid if t is larger than 50 in absolute value or if v is larger than 120 or less than 3 (you may assume that the values you get are in that range).
Resources for some of these assignments:
[spoiler title=’Math.random()’]
/**
* An itty bitty program to learn about Math.random()
* GE
* 9/28/2017
*
*/
public class MathRandTest_GE
{
public static void main(String []args)
{
for (int i = 0; i < 100; i++)
{
System.out.println(Math.random());
}
}
}
[/spoiler]
[spoiler title='Scanner Class']
/**
* good resource: http://docs.oracle.com/javase/tutorial/essential/io/scanning.html
* @author gracielaelia
* Problem: Both hasNext and next methods may block waiting for further input.
* hasNext() doesn't return false ever!!!! next() blocks until something is input!
* As you're reading from stdin, that'll either be when you send an EOF character (usually ^d on Unix),
* or at the end of the file if you use < style redirection.
* You cannot easily send and EOF character using the keyboard"
* -- usually Ctrl+D on Linux/Unix/Mac
* or Ctrl+Z on Windows does it
*/
import java.util.Scanner;
public class ScannerTest_GE{
public static void main(String [] args)
{
Scanner scan = new Scanner(System.in);
String name; // just a declaration
double base, exponent;
System.out.println("Enter the base ");
base = scan.nextDouble();
System.out.println("Enter the exponent ");
exponent = scan.nextDouble();
System.out.println("Enter your name ");
name = scan.next();
System.out.println(name + " the value is " + Math.pow(base,exponent));
System.out.println(name + " the integer value is " + (int)Math.pow(base,exponent));
}
}
[/spoiler]
Classwork:
Write a program, LoanPayment_YI.java to take the 3 arguments below (PV, r and n) and prints the payment, P.
