Exceptions, String, Wrapper - Things you need to learn

[admin]

1. Exceptions
In Study View tree, under "Study Refs" node, you will see an "ExceptionClassSummary" document. It lists and explains the exceptions that you need to know about.
(You may also download the document from here: http://enthuware.com/downloads/Exceptio ... ummary.pdf )
Briefly:

• Throwable
  Error and
  Exception
  RuntimeException
  
  ArrayIndexOutOfBoundsException
  ClassCastException
  NullPointerException
  ExceptionInInitializerError
  StackOverflowError
  NoClassDefFoundError
  
  IllegalArgumentException
  IllegalStateException
  NumberFormatException
  AssertionError

2. Methods in String, you need to learn about

• substring
  replace
  charAt
  indexOf
  length
  toLower/UpperCase
  compareTo
  equals
  equalsIgnoreCase
  contains
  endsWith
  startsWith
  valueOf
  trim

Almost all are very straight forward and their names tell you what they do.

StringBuilder/Buffer

• All 4 constructors.
  append
  delete
  insert
  indexOf
  length
  replace
  reverse
  substring
  setLength

All very straight forward methods.

3. Wrappers

• equals
  toBinaryString, toHexString
  valueOf
  parseInt/Byte etc.
  toString
  equals/compareTo

4. ArrayList

• add
  addAll
  remove
  removeAll
  sublist
  retainAll
  get
  contains
  clear
  size

Similar methods for HashSet as well. Make sure you understand how a Set (and HashSet) behave when you add duplicate elements. How it checks for duplicity.

HTH,
Paul.

[gparLondon]

1> Do we really have to know about set and its behavior?

2> What about ensureCapacity() method in ArrayList and StringBuilder/Buffer? Do we don't have to know about it? and the method capacity() is only there in StringBuilder/Buffer, but not in ArrayList.

3> There is a setLength() method only in StringBuilder/Buffer? Am I right?

4> Which is thread safe? String, StringBuilder, StringBuffer,Array, ArrayList?

[admin]

1. Yes.
2. Not a must but good to know.
3. Yes, but please check the JavaDocs for such questions because there could be a class that you are thinking about but I am not that has this method.
4. StringBuffer. Not sure what you mean by "Array". If you mean a regular array, there are no add/remove "methods" in an array. String is immutable so no question about anyone modifying it.

[toolforger]

Threading-wise, Java arrays with their element slots behave just like Java objects with public instance variables, so no, they are not thread-safe at all.

[aar2416]

Which array functions we need to know for OCA se 7?

[admin]

All. You need to read about all of the concepts about arrays. Follow any good book and read its chapter on arrays. That should be enough.

[aar2416]

All. You need to read about all of the concepts about arrays. Follow any good book and read its chapter on arrays. That should be enough.

thanks

[flex567]

Can you add what do we need to know about the Date API?

[admin]

Classes: java.time.LocalDateTime, java.time.LocalDate, java.time.LocalTime, java.time.format.DateTimeFormatter, java.time.Period
1. Constructors, static methods (now/of/from), and atXXX that deal with the creation of above classes.
2. parsing dates to/from date/string objects.
3. comparison of dates

Not really possible to list all the method names here because there are too many of them. Check out the Javadoc or go through Section 12.3 of OCAJP8 Fundamentals book by Hanumant Deshmukh.

[flex567]

Are these all the methods we need to know for the exam?

DATE API

LocalDateTime.now();
LocalTime.now();
LocalDate.now();

static LocalDateTime from(TemporalAccessor temporal)

LocalDate:

static LocalDate of( int year, int month, int dayOfMonth)
static LocalDate of( int year, Month month, int dayOfMonth)

LocalTime:

static LocalTime of( int hour, int minute)
static LocalTime of( int hour, int minute, int second)
static LocalTime of( int hour, int minute, int second, int nanoOfSecond)

withMonth
withDayOfMonth
withYear
withHour

atTime
atDate
atZone
now

static LocalDate parse(CharSequence text)
static LocalDate parse(CharSequence text, DateTimeFormatter formatter)


java.time.format.DateTimeFormat
ISO_DATE
ISO_TIME
ISO_DATE_TIME
ISO_LOCAL_DATE_TIME

Period:
static Period of( int years, int months, int days)
static Period ofDays( int days)
static Period ofMonths( int months)
static Period ofWeeks( int weeks)
static Period ofYears( int years)

parse

static Period ZERO

equals
isZero
isNegative

-----------------------
plusDays
plusWeeks
plusMonths
plusYears
minusDays
minusWeeks
minusMonths
minusYears

plus( long amountToAdd, TemporalUnit unit)
plus( TemporalAmount amountToAdd)
minus( long amountToSubtract, TemporalUnit unit)
minus( TemporalAmount amountToSubtract)

withMonths
withDayOfMonth
withYears

negated

DateTimeException

DateTimeFormatter

static ofPattern(String pattern)
static ofPattern(String pattern, String locale)

format(DateTimeFormatter dtf)
ofPattern

static DateTimeFormatter ofLocalizedDate(FormatStyle dateStyle)
static DateTimeFormatter ofLocalizedDateTime(FormatStyle dateTimeStyle)
static DateTimeFormatter ofLocalizedDateTime( FormatStyle dateStyle, FormatStyle timeStyle)
static DateTimeFormatter ofLocalizedTime( FormatStyle timeStyle)

FormatStyle.FULL
FormatStyle.MEDIUM
FormatStyle.SHORT
FormatStyle.LONG

equals(Object obj)
compareTo
isAfter/ isBefore / isEquals

[admin]

Wow...great effort. Yes, that should be it. Hope you haven't missed any Unless you want me to verify that you haven't missed anything
-Paul.

[flex567]

I didn't verify, and the list could be refined a bit as well.
Maybe some of the methods are missing and I think some should be removed?