Lecture 6, CS 302-6, September 16

1. Review
1. Variable assignments
2. Constants
3. I/O
4. Arithmetic

i. Clarification from last time – Math.pow(3,-2)

ii. Quadratic formula example – Quad.java

2. Random Class
1. Difference between Random and Pseudorandom

i. pseudorandom vs random

1. Humans are (maybe?) capable of random, computers cannot do random

ii. http://www.fourmilab.ch/hotbits/

1. This is based on radioactive decay, and is truly random

2. Using the random class:

i. import java.util.Random;

ii. Initialize

1. Unseeded:

a. Random rand=new Random()

2. Seeded

a. Random rand=new Random(long)

b. The value for the long determines what rand generates

iii. rand.nextInt, rand.nextDouble, etc to get values

1. nextInt(); //anywhere in int range (-2,147,483,648 to 2,147,483,648)

2. .nextDouble(); //vallue between 0.0 and 1.0

iv. 20 sided Dice Example – D20.java

3. Formatted Output
1. System.out.printf(“Price:%10.2f”,x)
2. See textbook for more details
4. Strings
1. Strings are sequences of characters. Examples:

i. “a”

ii. “c”

iii. “1”

iv. “&”

v. “ “

2. String name=”Rob”

i. name is variable, “Rob” is literal

1. ‘literal’ refers to the value stored in a variable

3. String length

i. Use string.length() to get number of characters in a string.

1. String name=”Rob”;

2. System.out.println(name.length()); // 3

3. String hello=”Hello World!”;

4. System.out.println(hello.length()); // 11

4. Empty String

i. String empty=“”; //Length=0

5. Concatenating strings

i. Like addition, but for Strings

1. int+String or String+int both create Strings

6. Reading String input

i. Scanner in=new Scanner();

ii. in.next(); gets one word

iii. in.nextLine(); – whole line (multiple words)

iv. So, if the input is “Hello World!”:

1. in.next()->”Hello”

2. in.nextLine()->”Hello World!”

7. Parsing numbers from strings

i. int count=Integer.parseInt(string)

ii. double price=Double.parseDouble(string)

iii. This works only for strings like “123”, “123.12”, etc.

iv. If Java can’t translate the string, we get a run-time error

1. Integer.parseInt(“Hello World!”);

2. Integer.parseInt(“Two”);

8. Escape sequences

i. These can be used to print characters that aren’t ‘easy to print’

1. \” //prints “

2. \\ //prints \

3. \n //prints new line

9. Characters

i. theString.charAt()

ii. The first character in a string is 0, second is 1, etc.

iii. String name=”Rob”

1. Character 0 is “R”

2. Character 1 is “o”

3. Character 2 is “b”

4. System.out.println(name.charAt(1)); //Prints “o”

10. Substrings

i. theString=”STRING”

ii. theString.substring(1,4)=”TRI”

iii. theString.substring(0,1)=”S”

iv. theString.substring(4)=”NG”

1. if the second argument isn’t provided, the substring will go until the end of the string

5. HW
1. Read 3.3-3.4
2. Optional exercises – R2.1,R2.8,R2.13R2.16,p2.2,p2.12