Lecture 4

Fall 2018

Narges Norouzi

Recap

  • User Input

  • Conditionals

    • if-statement

    • Nested if-statements

    • switch-case statements

  • Loops

    • while loop

    • do-while loop

    • for loop

Break & Continue

  • Break:
    • Jumps out of a block

 

 

 

  • Continue:
    • Jumps to the beginning of the block

Arrays

Array

  • Indexed sequence of values of the same type

  • Example:

    • 52 playing cards in a deck

    • 1 million characters in a book

    • 130 students in this course sorted by their ID

https://docs.oracle.com/javase/tutorial/java/nutsandbolts/arrays.html

Many Variables of Same Type

Goal: 10 variables of type int

Many Variables of Same Type

Goal: 10 variables of type int

Declares, creates, and initializes values

Arrays in java

  • To make an array, declare, create and initialize it.​

  • To access element 'i' of an array named ‘a’, use a[i].​

  • Array indices start at 0.

Example

compact alternative

  • Declare, create, and initialize in one statement.

  • Default initialization: all numbers automatically set to 0.

Explicit Initialization

  • Example

 

 

 

 

  • Equivalent to

Demo

Dot product of two vectors

Length of the array

  • We can get the length of the array using the length field:

 

 

 

  • Can be used for iteration over array elements

 

Consider

​

 

 

 

  • Defined an array to reference a list of 100 integers
  • Each element is initialized by default to 0
  • Two exceptions will be thrown here:
    • -1 is not a valid index – too small
    • 100 is not a valid index – too large
      • IndexOutOfBoundsException

Break

LINK

Multi-dimensional Arrays

Two-dimensional array

  • Examples:

    • Table of grades for each student and assignment

    • Table of data for each experiment and outcome

  • Mathematical abstraction: Matrix

  • Java abstraction: 2D array

Two-dimensional arrays in java

  • Array Access: use a[i][j] to access element in row i and column j.

 

  • Zero-based indexing: Row and column indices start at 0.

2D array or Array of Arrays

Example

Demo

Matrix Addition

Zybooks chapters we covered

  • Chapter 4 part 4.9
  • Chapter 5 up to and including 5.9