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97 lines
1.8 KiB
Markdown
97 lines
1.8 KiB
Markdown
# Lecture in CPSC 220 Sept 25 2017
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## Constants
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Adding the keyword `final` in front of a variable declaration makes the variable constant. Meaning you cannot later change it in the code.
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```java
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final int MAX = 10;
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```
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By industry norm, the style of the variable is to have it in all caps.
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You CANNOT do the following
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```java
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final int MAX = 10;
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MAX = 15;
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```
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## Using Libraries
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1. Import the library
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2. Find the method that is appropriate
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3. Use it
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Example:
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```java
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import java.util.Math;
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public class MathTest {
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public static void main(String[] args) {
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double answer = Math.ceil(5.4);
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System.out.println(Math.ceil(4.5));
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}
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}
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```
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## Typecasting / Type Conversions
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You can only cast a variable if you are casting it to a type that is larger than the one it was previously. The expression Polack used is that you cannot fit into super skinny jeans, but you can fit into bigger pants.
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```java
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double dnum;
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float fnum;
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int inum;
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dnum = (double)fnum * (double)inum;
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```
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## Char vs String
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`String`s are initialized in Java with double quotes while `char`s are initialized with single quotes
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```java
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char initial = 'j';
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String name = "Jennifer";
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```
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Characters can be read in as an integer.
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## Random Numbers
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1. Import `java.util.Random;`
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2. Declare the random number generator
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3. Initialize with `new`
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4. Use it
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```java
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import java.util.Random;
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public class RandTest {
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public static void main(String[] args) {
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Random rand;
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rand = new Random();
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int number = rand.nextInt(100); // Random generates number between 0-99
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}
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}
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```
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How do you generate numbers in a different range? [50, 150]
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```java
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rand.nextInt(100); // 0-99
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rand.nextInt(101) // 0 - 100
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rand.nextInt(101) + 50 //50-150
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```
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In more general terms
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```java
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rand.nextInt(end - start + 1) + start
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```
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