Arrays/Java

Notes

Notes from Goodrich et al Data Structures in Java Chapter 4

Basics of Arrays

Building an array to hold a basic object - a GameEntry representing a high score entry in a game.

Link: https://charlesreid1.com:3000/cs/java/src/master/arrays/GameEntry.java

The default array element will be null, so an empty array of GameEntry objects contains null pointers

Java stores references to addresses in memory, so these objects are like remote controls.

Sorting an array

Simple sort method: insertion sort (not the fastest, but simple)

Indexing, algorithm implementation, illustration of god practice

Java Array utilities

Array class static methods:

• equals(A, B)
• fill(A,x)
• copyOf(A, n)
• copyOfRange(A,s,t)
• toString(A)
• sort(A)
• binarySearch(A,x)

Random numbers:

• nextInt() - next random integer somewhere in the range of all possible integers
• nextInt(n) - between 0 and n, non-inclusive
• nextDouble() - uniform, between 0 and 1
• nextGaussian() - gaussian random, mean 0 std 1

Easy way to get a copy of an array:

• A.clone()

Converting between Strings, chars, and ints:

• Caesar cipher and basic cryptography
• String objects have a toCharArray method to turn String into char[]
• Strings have constructor to turn char[] into String: new String(char_arr)
• Simplest and most general way is probably to use 2 Strings, fwd and reverse, and lookup action
• Char/int math, though, allows us to do it just as fast, and with mod math right there.

Implementing a Caesar Cipher class:

• What are the inputs? Constructor taking a key
• What are the private variables? encryption string, decryption string
• Encrypt takes String parameter, return transform(message, encryption string)
• Decrypt takes String parameter, return transform(ciphertext, decryption string)
• Transform takes orig, alphabet, does char ops on it.