Lab 1 Slides

# SSUI Mobile Lab (Spring 2019)
## Week 1: Java Refresher

.title-slide-logo[
  ![Android Logo](java/android-logo.png)
]

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# Quick Java Refresher

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## What is Java?
--

- Strongly, statically typed language

- Every variable has a type
  - This type is decided at compile time (mostly)

- Compiled, class-based, Object-oriented

- Platform agnostic

- __Write once__, _run anywhere_ without recompilation
  - Especially useful for Android

---

## Java Basics: Primitive Types

--
- Boolean

```java
boolean hasClassStarted = true;
boolean isClassOver = false;
```

--
- Integer

```java
int numStudents = rand.nextInt(0, 30);
```

--
- Float

```java
float gradePointAverage = 3.2f;
```

--
- Double
  - Higher precision than float

```java
double examScore = 97.362;
```

--
- Byte, Short, etc.

---
## Java Basics: Text

--
- Characters

```java
char section = 'B';
```

--
- Strings

```java
String instructor = "Jennifer Mankoff";
```

--
All non-primitives types inherit from `Object` class
  - Including `String`; note the capitalization

---
## Java Basics: Visibility Modifiers

```java
public final String course = "CSE 340";
///...
private final String ssn = "123-45-6789";
```

--
- `private`
  - Kept secret, can only be read/written by `self`
  - Cannot be accessed by subclasses

--
- `package private`
  - This is the default access if no modifier is specified
  - Accessible by all classes in the same package.

--
- `protected`
  - Access restricted to `self`, subclasses, and package

--
- `public`
  - The world can read/write (fields) or call (methods)

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## Java Basics: Visibility Modifiers

--
  - Generally, you want to be as restrictive as possible
    - Usually, this means `private`

- Create getter/setter methods to modify the member variables

- .red[__Almost never use__ `public`] for fields
    - Except for constants

---
## Java Basics: `final`

--
- Prevent value from changing after initialization

```java
final double courseGrade = 95.0; // cannot be modified ever!
```

--
- Prevent subclassing

```java
  public final class Person {
      // can't subclass (for example to make a Student class)
      // ...
  }
```

--
- Prevent overriding

```java
  public final int getValue() { // can't override!
      return 0;
  }
```

---
## Java Basics: `static`

--
- Use for constants that are the same for all instances of a class

```java
static double SALES_TAX_RATE = 0.07;
```

--
- Methods that can be called without an class instance

```java
static String toString(int i);
// For example Integer.toString(100) => "100";
```

--
- By convention, names are capitalized and snake_cased

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## Java Basics: Methods
- Methods in Java typically follow this format:

```java
{visibility} [static] [final] returnType methodName(paramType paramName, ...) {
    // ...
}
```

--
- `static` and `final` are optional, special modifiers
- `visibility` is one of `public`, `private`, `protected`, or empty for package private

---
## Java Basics: Method Example

Summing two numbers and returning the answer as a string

```java
public String getSumOfTwoNumbersAsString(int first, int second) {
  int sum = first + second;
  return Integer.toString(sum);
}
```

---
## Java Basics: Declaring a class

```Java
{visibility} class ClassName {
  // Field declarations

// Method definitions
}
```

---
## Java Basics: Constructing a Class

```java
public class Student {

// Class (static) variables -
  public static final String STUDENT_KEY = "STUDENT";
  private static final String ID_PREFIX = "S";

// Instance Variables
  private String idNumber;
  private String name;

// Constructors - used to create an instance
  Student(String name, String idNumber) {
    this.name = name;
    this.idNumber = idNumber;
  }

// Methods
  public String getPrefixedIdNumber() {
    return ID_PREFIX + idNumber;
  }
```

---
## Java Basics: Constructing a Class cont.
```java
  // Getter
  public String getName() {
    return name;
  }

// Setter
  public void setName(String newName) {
    if (newName == null || newName == "") {
      newName = "Unknown";
    }

name = newName;
  }

// ... etc.

}
```

---
## More Java Resources

- Java Documentation (https://docs.oracle.com/javase/8/docs/api/)

- __Online Java Practice Problems__:

- http://codingbat.com/java

- https://practiceit.cs.washington.edu/problem/list