CSC1110 - Java Basics

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layout: true
class: taylor msoe
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.title[
  # Java Basics
]

???

* **P** speaker view
* **C** clone slideshow
* **?** help

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# Creating and Running a Java Program

* Write Java program in a text file with `.java` extension

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* Compile the program

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* Run the program with a Java Virtual Machine (JVM)

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# Typical Steps in Software Development

* Requirements analysis

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* Design

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* Implementation

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* Testing

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* Documentation

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* Maintenance

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# Program Overview

* All Java code is organized into `.java` files containing a **class**

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* Class name and file name just match

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* Each program has one `main()` method that specifies instructions
``` Java
    public class ClassName {
        public static void main(String[] args) {
            // ...
        }
    }
```

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* A **method** is a sequence of instructions to be performed
    + To start, our programs will have one class and one method (the `main()` method)

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# Representing Data

* Programs consist of instructions that act upon data within the program

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* Data is represented as a sequence of bits (e.g., 00010011011101001)

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* Each piece of data has a type associated with it

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* Java uses the type to determine how to interpret the bits

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* Data in our programs can be specified as a literal value
  + `3` — is an integer literal
  + `3.8` — is a double-precision floating point literal
  + `'a'` — is a single character literal
  + `"and"` — is a string literal

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# Variables

* A variable is a name associated with a piece of data in our program

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* Names must follow identifier rules (simplified)
  + Begin with a letter
  + Can contain letters, digits, and underscores
  + Are case sensitive
  + Must be unique and cannot be Java keywords

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* Each variable must have a type associated with it

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* We declare a variable by indicating its type followed by the desired name
``` Java
int i;
```

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* Java has several built-in types (called **primitives**)

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# Primitives

* `int` — integer (32 bits representing values between -2 billion and 2 billion)

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* `double` — double-precision floating point number (64 bits representing a number with a decimal point)

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* `char` — character value (16 bits)

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* `boolean` — true or false

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* `byte`, `short`, and `long` — integers (8 bits, 16 bits, and 64 bits, respectively)

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* `float` — floating point number (32 bits representing a number with a decimal point)

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# Reference Types

* Java also supports non-built-in types, e.g., `String`, `Scanner`

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* Here the variable holds a memory address where the actual data is stored

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* Reference types refer objects which hold data

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* The objects may have methods (behaviors) that can called to act on the data