Accessible methods in the Java Quick Reference

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Object

• boolean equals(Object other)
• String toString()

Integer

• Integer(int value)
• int intValue()
  • returns value in int
• Integer.MIN_VALUE
  • smallest value that can be stored in an int
• Integer.MAX_VALUE
  • largest value that can be stored in an int

Double

• Double(double value)
• double doubleValue()

String

• int length()
• String substring(int from, int to)
• String substring(int from)
• int indexOf(String str)
• int compareTo(String other)
  • returns
    • 0 if equivalent
    • some number > 0 if earlier in alphabet
    • some number < 0 if later in alphabet

Math

• abs(int/double x)
• pow(double base, double exponent)
• sqrt(double x)
• double random()
  • double in the range [0,1)

List<E>

• int size()
• boolean add(E obj)
  • returns true after adding it ._.
• void add(int index, E obj)
• E get(int index)
  • if it’s a number, returns Integer/smth else
    • (not int/double, but Integer/Double)
• E set(int index, E obj)
• E remove(int index)
  • changes indices of next elements. BEWARE IN LOOPS

TERMS

========

• API = Application Programming Interface
  • methods, routines, etc used to program
• nested/inner class

    class foo {
        class bar {...}
    }
  

  • ^^ bar is nested class
  • bar sees everything from foo, but isn’t a foo
  • ex: String is a nested class of Object
• child class
  • class bar extends foo {...}
  • ^^bar is child class
  • bar sees everything from foo, and is a foo

KEYWORDS

===========

implements

• for interfaces (methods not defined)
• provide definitions for APIs

extends

• for Classes (methods defined)
• parent-child relationship

static

• modifies/takes stuff from the class
• nonstatic (aka not putting static there) modifies the instance

Integer/Double

• can == null => can’t assign null to an int
  • otherwise, it’s the same as int/double in Java 5+

List

• from index 0
• see methods
• to initialize
  • List<Integer/etc> a = Arrays.asList(ele1, ele2, ...);
• is immutable (cannot be modified)
• is an interface

ArrayList

• extends AbstractList that extends List
• from index 0
• to initialize
  • ArrayList<Integer/etc> a = new ArrayList(Arrays.asList(ele1, ...);
• is a Class

CONTROL STATEMENTS

=====================

• enhanced for loop (“for-each”)

    String[] array = {...};
    for (String element : array) {
        //do something for all elements in array
    }
    the same as:
        for (int i=0; i<array.length(); i++) {
            ;
        }
  

SORTS

========

• insertion sort
• selection sort
• bubble sort
• mergesort
• heapsort
• quick sort

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Java unrelated to APCS

• concurrency
  • processes happen at the same time
  • use threads
• immutable
  • that instance cannot be changed after it is made
  • uses the keyword final
• \unnnn (escape sequence like \n)
  • line break LOL
• assert <boolean expression>
  • check for bugs in the code
  • if expression after it is false, it stops the program
  • ex: assert varIsTrue == false