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OCA Java Programmer I (operators (logical operator (short-circuit…

- - - - || if the left side is true so the right side is no calculated
- - - - charAt
      - indexOf
      - length
      - substring
      - append
      - insert(0,"-") -> -animal
      - delete(1,3) -> animal
      - deleteCharAt(0) -> nimal
      - reverse
      - toString
    - - can have append on constructor as new StringBuilder.append("ab");
  - - - .trim(" abc ") --> takes off \t \n \r
      - .replace('a', 'A') --> "AbcAbc"
      - .contains("abc") --> true/false
      - .startsWith("a") endsWith("c") ->> true/false
      - .equalsIgnoreCase("TeXt")
      - .equals("text")
      - .toLowerCase() and toUpperCase()
      - .substring(3) or (3,4) ->> (3,3) = empty, (3,2) exception
        return the string starting from the requested index and stops right before of requested end index
      - .indexOf("char or string", "from position"). Return -1 if not found
      - .charAt(position)
      - .length()
      - Index from 0
    - - without new. New will tell JVM to do not use string pool
      - Literal values as "name"
    - - a = "ab" --> a = "bc" --> "ab" will to garbage collection
      - are final
      - just getters
    - - left to right
      - "c" + 2 + ' > "c21"
      - 1 + 2 + "c" > "3c"
  - - - Arrays.sort(arrayObject) - String will order number as non numbers
      - Arrays.binarySearch(array,"value") -> return index (although, it works properly just for sorted array, it can not be predicted for unsorted
      - List<String> x = Arrays.asList(array) \ convert an array to a list (pay attention, the size of the list cannot bet changed
    - - import java.util.ArrayList
      - ArrayList<String> x = new ArrayList<>(); or new ArrayList<String>() as java 5
      - Implements List interface so -> List<String> x = new ArrayList<String>();
      - ArrayList x = new ArrayList(); stores everything, except primitives
      - methods
        
        add("value") or add(position, value). It will not replace just insert
        
        remove(value) just the first one or remove(index) can throw an outbound exception
        
        set(index, value) can throw an outbound exception
        
        isEmpty(), size(), clear()
        
        contains(value) \ true or false
        
        equals(value) \ compare each element value
        
        toArray(), return Object[], if you wish new array = arraylist.toArray(new String[0])
        
        sort: Collections.sort(List) (use Collections class)
      - wrapper
        
        int primitive = Integer.parseInt("123");
        
        Integer wrapper = Integerg.valueOf("123";
        
        Just Character has no Wrapper class
        
        pay attention on remove method, if you type remove(1) it will remove the index, you should type remove(new Integer(1))
  - - - LocalDate date = LocalDate.of(2015,Month.JANUARY,20) or 1 replacing JANUARY
      - LocalTime time = LocalTime.of(6,15, 30) // 6 hours and 15 minutes and 30 seconds
      - LocalDateTime dateTime = LocalDateTime.of(date,time) or (2015,1,20,6,15,30)
    - - date = date.plusWeeks(1)
        plusDays(2)
        plusMonths(4)
        plusYears(5)
        minus...
        pay attention there is no plusMinute on LocalDate
      - isBefore(LocalDate)
      - plus(period)
      - parse("11:00");
        parse("11:00",formatter);
    - - Period period = Period,ofMonths(3) // 3 months
      - Period period = Period.ofDays(4) // 4 days
      - Period perido = Period.of(1,0,7) // Every year seven days
      - period.of is a static method and cannot be chained as period.ofMonths(1).ofYears(2)
    - - package java.time.format
      - date.format(DateTimeFormatter.ISO_LOCAL_DATE)
      - time.format(DateTimeFormatter.ISO_LOCAL_TIME)
      - DateTimeFormatter short = DatetimeFormatter.ofLocalizedDate(FormatStyle.SHORT);
        short.format(date) // 1/20/18
      - On exam: SHORT and MEDIUM
      - DateTimeFormatter f = DateTimeFormatter.ofPattern("hh:mm);
- - - - Just one class should be public and should has the file name
      - Can have multiple classes
    - - Instance variable dos not have static (Will be in scope until the Object ends)
      - local scope {...}
      - Default
        
        object: null
        
        char: '\u0000' (NUL)
        
        float, double: 0.0
        
        byte, short, int, long: 0
        
        boolean: false
      - you shouldn't initialize them (they have a default value) but you should initialize local variables
      - Class variable should have the keyword static (Will be in scope until the program ends)
    - - Can't have @ or *
      - Can have letter, _, $ and digit
      - Must begin with
        
        Not a number
        
        _
        
        $ (but do not use to start class)
        
        Letter
  - - - All references are the same size, the objects is the entity in the memory
      - can accept null
      - point to an object in memory instead of the value in memory as primitive does
    - - digit types
        
        "_" can separate digits as 100_000_000
        
        binary: 0b11 > 3
        
        hexa: 0xFF > 31
        
        octal: 017 > 15
      - char: 16-bit unicode
      - double: 64-bit float
      - float: 32-bit float (123.4f)
      - long: 64-bit int (1111111111L)
      - int: 32-bit int (2,147,483,647)
      - short: 16-bit int
      - byte: 8-bit int
      - boolean: true/false