Chapter 2 - Java operators

Question 1

What are the three flavors of operators available in Java?

Answer 1

three flavors of operators are available in Java: unary, binary and ternary.

Question 2

What is the order Java operators follow?

Answer 2

Java operators follow order of operation. If 2 operators have the same level of precedence, then Java guarantees left-to-right evaluation.

Question 3

Arithmetic operators may be apply to? And except to which type?

Answer 3

All of the arithmetic operators may be applied to any Java primitives. EXCEPT boolean and String.

Question 4

Which are the only arithmetic operators that can be applied to Strings?

Answer 4

Only the addition operators + and += may be applied to String values, which result in String concatenation.

Question 5

In numeric promotion, if two values have different data types, what Java does?

Answer 5

If two values have different data types, Java will automatically promote one of the values to the larger of the two data types.

Question 6

In numeric promotion, if one of the values is integral and the other is floating point, what will Java do?

Answer 6

If one of the values is integral and the other is floating-point, Java will automatically promote the integral value to the floating-point value’s data type.

Question 7

In numeric promotion, to which type are smaller data types (byte, short and char) promoted to?

Answer 7

Smaller data types, namely byte, short and char, are first promoted to int any time they’re used with Java binary arithmetic operator, even if neither of the operands is int. **important: unary operators are excluded from this rule. I.e: applying ++ to a short value results in a short value.

Question 8

What is the resulting value after a promotion has been done and all the operants have the same data type?

Answer 8

After all promotion has occurred and the operands have the same data type, the resulting value will have the same data type as its promoted operands.

Question 9

When references are equal?

Answer 9

Two references are equal if and only if they point to the same object, or both point to null.

Question 10

Which data types are supported by Switch statements?

Answer 10

Data types supported by switch statements:

byte and Byte 
short and Short
char and Character
int and Integer
String
enum values

Question 11

Are boolean and long supported by Switch statements?

Answer 11

No. Boolean and long and their associate wrapper classes are not supported by switch statements.

Question 12

What is the variable’s coverage in the initialization of a FOR loop?

Answer 12

Variables declared in the initialization block of a for loop have limited scope and are only accessible within the for loop.

Question 13

Does below code compile? If so, which will be the output?

for ( ; ;) {
}

Answer 13

The above will compile and run without issue. The output is an infinite loop.

Components of the for loop are each optional BUT the semicolons ; are required as for ( ) will not compile.

Question 14

In a FOR loop, can a variable be redeclare in the initialization block (i.e. x below)

int x = 0;
for(long y = 0, x = 4; x < 5 && y < 10; x++, y++){
}

Answer 14

No, the above will not compile because x is initialized 2 times; outside of the for and inside the for statement.

Question 15

Can different data types be used in the initialization block of a FOR loop?

for(long y = 0, int x = 4; x < 5 && y < 10; x++, y++){
}

Answer 15

No, the variables in the initialization block must all be of the same type.

Question 16

Can loop variables be used outside the loop?

for(int y = 0, int x = 4; x < 5 && y < 10; x++, y++)
{
}

System.out.print(x);

Answer 16

No. Using loop variables outside the loop make the code to not compile. In the above example x is a local variable to the for and cannot be outside.

Question 17

What are the concatenation rules?

Answer 17

1. If 2 numbers are involved, use numeric addition.
2. If strings and numbers are involved, use concatenation.
3. Evaluate the expression from left to right.

Question 18

Is String mutable or immutable?

Answer 18

String is immutable meaning it cannot be changed once it is created.

Also final is immutable.

Question 19

What does the String pool contain?

Answer 19

Also known as “intern pool”. Contains literal values that appear in your program.

Example:

String name = “Fluffy”

Question 20

What does lenght() do?

Answer 20

lenght( )

Counts the number of characters in a string. It counts from 1 to n.

Question 21

Does lenght() consider what is in an array or how many slots have been allocated?

Answer 21

Length does not consider what is in the array; it only considers how many slots have been allocated.

Question 22

While using indexes or positions within a list Java counts starting at which position?

Answer 22

Starting at zero (0).

Question 23

What does IndexOf( )do?

Answer 23

IndexOf( )

This method looks at the characters in the String and finds the first index that matches the desired value.

Question 24

What is the value returned by the IndexOf() method if a match is not found?

Answer 24

IndexOf() does not throw an exception if a match is not found. It returns -1 instead.

Question 25

What does substring() do?

Answer 25

Substring( )
Looks for characters in a string.
The first parameter is the index to start which is a zero-based index.

There is an optional second parameter which is the end of the index you want to stop at (it is not included in the returned string).

Question 26

What does substring(3, 3) return having below String?

animals

Answer 26

Having this string: animals

…substring(3, 3) returns empty string because there are no characters in the middle.

Question 27

What does substring(3, 2) return having below String?

animals

Answer 27

substring(3, 2) throws an exception because the end index cannot be less than the initial index.

Question 28

What does substring(3,8) return having below String?

Animals

Answer 28

substring(3,8) throws an exception because the original string does not have position 8.

Question 29

What does substring(3, 7) return having below String?

Animals

Answer 29

substring(3, 7) does not throw an exception because there is the “end of string” invisible position.

Question 30

Is StringBuilder mutable or immutable?

Answer 30

The StringBuilder class is immutable.

Question 31

Does == check object equality or the values inside the String?

Answer 31

== checks object equality.

Question 32

What does equals check?

Answer 32

The equals method checks the values inside the String instead of the object reference.

Question 33

When are Strings evaluated?

Answer 33

Strings are evaluated at compile-time, for that reason below Strings are different even though at run time evaluate to the same String:

String x = “Hello World”;
String y = “ Hello World.trim();

Question 34

Does StringBuilder include the equals method?

Answer 34

StringBuilder DOES NOT include the equals method.

Question 35

Can a StringBuilder be compared (==) with a String?

Answer 35

Java does not allow to compare a String with StringBuilder using ==. The code does not compile.