What is Java?

• Strongly, statically typed language

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

Java Basics: Primitive Types

Java Basics: Primitive Types

boolean hasClassStarted = true;
boolean isClassOver = false;

int numStudents = rand.nextInt(30);

Java Basics: Primitive Types

boolean hasClassStarted = true;
boolean isClassOver = false;

int numStudents = rand.nextInt(30);

float gradePointAverage = 3.2f;

Java Basics: Text

Java Basics: Visibility Modifiers

public final String COURSE = "CSE 340"; 
...
private final String SSN = "123-45-6789";

Java Basics: Visibility Modifiers

public final String COURSE = "CSE 340"; 
...
private final String SSN = "123-45-6789";

Java Basics: Visibility Modifiers

public final String COURSE = "CSE 340"; 
...
private final String SSN = "123-45-6789";

Java Basics: Visibility Modifiers

Java Basics: final

Java Basics: final

// local variable cannot be modified ever!
final double courseGrade = 95.0;

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

Java Basics: static

Naming Conventions

• class names are PascalCased
• local variables and method names are camelCased
• class or instance variables begin with a 'm' (for member), such as mTotalAmount
• constants are UPPER_SNAKE_CASED

Java Basics: Methods

• Methods in Java typically follow this format:

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

Java Basics: Method Example

Summing two numbers and returning the answer as a string

public String getSumOfTwoNumbersAsString(int first, int second) {
  int sum = first + second;
  return Integer.toString(sum);  // could also return "" + sum
}

Java Basics: Declaring a class

{visibility} class ClassName {
  // Field declarations
  // Method definitions
}

Java Basics: Constructing a Class

public class Student {
  // Class (static) variables -
  public static final String STUDENT_KEY = "STUDENT";
  private static final String ID_PREFIX = "S";
  // Instance Variables
  private String mIdNumber;
  private String mName;
  // Constructors - used to create an instance
  Student(String name, String idNumber) {
    this.name = mName;
    this.idNumber = mIdNumber;
  }
  // Methods
  public String getPrefixedIdNumber() {
    return ID_PREFIX + mIdNumber;
  }

Java Basics: Constructing a Class cont.

  // Getter
  public String getName() {
    return mName;
  }
  // Setter
  public void setName(String newName) {
    if (newName == null || newName == "") {
      newName = "Unknown";
    }
    mName = newName;
  }
  ... // etc.
}

Enums

An enum type is a special data type that enables for a variable to be a set of predefined constant

public enum EssentialGeometry { INSIDE, OUTSIDE };
...
EssentialGeometry where = EssentialGeometry.INSIDE;

Switch Statements

A form of a conditional with different execution paths

public enum EssentialGeometry { INSIDE, ON_EDGE, OUTSIDE };
...
EssentialGeometry where = EssentialGeometry.INSIDE;
switch (where) {
  case ON_EDGE:
    // do the edgy things
    break;
  case INSIDE:
    // do the inside things but also fall through
    // and do the OUTSIDE things because no break statement;
  case OUTSIDE:
    // do the outside things
    break;
  default:
    // do default things
    // automatically falls through
}

More Java Resources

• Java Documentation (https://docs.oracle.com/en/java/javase/13/docs/api/)

• Online Java Practice Problems:

  • http://codingbat.com/java

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