Oca Java Se 8 Programmer I: Chapter 3 Core Java Apis

Front 1

What number does Java start counting String and Array indexes with?

Back 1

0

Front 2

What is the difference between "Hello" and new String("Hello")?

Back 2

Using a string literal adds the string to the string pool. Using the new keyword creates an object that goes on the heap.

Front 3

What happens if a string and a number are added together?

Back 3

The number will be converted into a string and the two strings will be concatenated

Front 4

What does it mean for an object to be immutable?

Back 4

Once the object is created it cannot be altered directly.

Front 5

True or False: A constructed string and a string in the string pool with the same characters in sequence will return equal when compared with ==

Back 5

FALSE. They are different strings in the pool and == checks reference equality

Front 6

True or False: A constructed string and a string in the string pool with the same characters in sequence will return equal when compared with the equals() method

Back 6

TRUE. String implements the equals method and uses it to compare the actual contents of a string.

Front 7

If strings are immutable, how do you change the value of a string variable?

Back 7

Assign the results of a string modifying method to the variable.

Front 8

What does String.length() do?

Back 8

Returns the number of characters in the string as an int

Front 9

What does String.charAt() do?

Back 9

Returns the character at the specified index

Front 10

If indexOf doesn't find any characters in the string that match the provided parameter, what value is returned?

Back 10

-1

Front 11

True or False: The character at the index specified by the first parameter of a substring is included in the results

Back 11

TRUE

Front 12

True or False: The character at the index specified by the second parameter of substring is included in the results

Back 12

FALSE, it stops before the character at the end index

Front 13

True or False: The end index parameter in a substring can be one greater than the actual max index

Back 13

TRUE

Front 14

If an ending index is not provided, what will substring return?

Back 14

A string starting with the provided start index to the end of the string

Front 15

What is the difference between the String and StringBuilder classes?

Back 15

String is immutable, while StringBuilder is not

Front 16

If a class hasn't implemented equals(), how does the method work?

Back 16

Uses the default == operator, which checks for reference equality

Front 17

What value will a binarySearch on an unsorted array return?

Back 17

The value is unpredictable and not useful

Front 18

What value will a binarySearch on a sorted array return if the target element is in the array?

Back 18

The index of the match

Front 19

What value will a binarySearch on a sorted array return if the target element is NOT in the array?

Back 19

The negative value where the target element would be minus 1

Front 20

True or False: An array can change size after it is instantiated.

Back 20

FALSE. An array's size is fixed once it is instantiated. An ArrayList however dynamically changes size as items are added.

Front 21

How do you create an ArrayList with a specified type?

Back 21

Using generics, which is declared with the diamond: operator <>

Front 22

How do you convert an ArrayList to an Array?

Back 22

toArray()

Front 23

How do you convert an Array to an ArrayList?

Back 23

Arrays.asLIst(arrayParameter)

Front 24

What is Autoboxing?

Back 24

Autoboxing is when Java automatically converts a primitive into the relevant wrapper class so it can be used by processes that require an object over a primitive

Front 25

What is a Wrapper Class?

Back 25

A Wrapper Class is a class that is the object form of a primitive data type

Front 26

When used on a string, what is the difference between parse and valueOf?

Back 26

Parse will convert the string into a primitive data type, while valueOf will convert the string into a wrapper class object

Front 27

How do you sort an Array?

Back 27

Arrays.sort()

Front 28

How do you sort an ArrayList?

Back 28

Collections.sort()

Front 29

How do you create a date/time object with the new LocalDate/Time classes?

Back 29

Use the static method of()

Front 30

True or False: The month index begins at 1 instead of 0.

Back 30

TRUE

Front 31

True or False: You can still create a date object with LocalDate/Time with the new keyword

Back 31

FALSE, all constructors are private and can only be accessed through the of() static method

Front 32

True or False: The LocalDate/Time classes are immutable

Back 32

TRUE, results of any methods which modify a date/time object must have their results assigned to a variable

Front 33

True or False: Period class instantiators cannot be chained because the methods are static.

Back 33

TRUE

Front 34

What are the 5 ways a Period object can be instantiated?

Back 34

ofYears, ofMonths, ofWeeks, ofDays, and of(Years, Months, Days)

Front 35

What is the Time equivalent of a Period?

Back 35

Duration

Front 36

True or False: You cannot apply a date modifier to a time only object.

Back 36

TRUE