Java

Controlling the Flow

Expressions
An expression is a construct made up of variables, operators, and method invocations, which are constructed according to the syntax of the language, that evaluates to a single value.
int cadence = 0; The data type of the value returned by an expression depends on the elements used in the expression. The expression cadence = 0 returns an int because the assignment operator returns a value of the same data type as its left-hand operand; in this case, cadence is an int.
Operators, Precedence, and Associativity
Operators are tokens that are used to combine values in expressions. When evaluating an expression, Java uses precedence and associativity rules to determine the order in which operators are applied. These rules mostly are derived from the C language precedence and associativity rules.
Java operators are listed in order of precedence with highest precedence at the top. The rows of the table define precedence groups. Two operators in the same group have the same precedence. Higher precedence operators are applied before lower precedence operators. Except for bitwise operators, the precedence rules give Java expressions the meaning that you would normally expect from experience with mathematical expressions. If an expression behaves contrary to your intention, you can always force a different order of evaluation using parentheses.
Associativity rules are only used to determine the order of evaluation for two operators that are in the same group. Most groups use left-to-right associativity, which means that in an expression with operators in the same precedence group, the operators are applied in left-to-right order. This is what we normally expect for operators that appear in between two operands.

operator group associativity type of operation

! ~ ++ -- + - right-to-left unary

* / % left-to-right multiplicative

+ - left-to-right additive

<< >> >>> left-to-right bitwise

< <= > >= left-to-right comparison

== != left-to-right comparison

& left-to-right bitwise

^ left-to-right bitwise

| left-to-right bitwise

&& left-to-right boolean

|| left-to-right boolean

?: right-to-left conditional

= += -= *= /= %= &=
^= |= <<= >>= >>>= right-to-left assignment

, left-to-right comma

Regular Expression
A regular expression is a special sequence of characters that helps you match or find other strings or sets of strings, using a specialized syntax held in a pattern. They can be used to search, edit, or manipulate text and data.
The java.util.regex package primarily consists of the following three classes:
* Pattern Class: A Pattern object is a compiled representation of a regular expression. The Pattern class provides no public constructors. To create a pattern, you must first invoke one of its public static compile methods, which will then return a Pattern object. These methods accept a regular expression as the first argument.
* Matcher Class: A Matcher object is the engine that interprets the pattern and performs match operations against an input string. Like the Pattern class, Matcher defines no public constructors. You obtain a Matcher object by invoking the matcher method on a Pattern object.
* PatternSyntaxException: A PatternSyntaxException object is an unchecked exception that indicates a syntax error in a regular expression pattern.
Regular Expression Syntax:: -

Subexpression Matches

^ Matches beginning of line.

$ Matches end of line.

. Matches any single character except newline. Using m option allows it to match newline as well.

[...] Matches any single character in brackets.

[^...] Matches any single character not in brackets

\A Beginning of entire string

\z End of entire string

\Z End of entire string except allowable final line terminator.

re* Matches 0 or more occurrences of preceding expression.

re+ Matches 1 or more of the previous thing

re? Matches 0 or 1 occurrence of preceding expression.

re{ n} Matches exactly n number of occurrences of preceding expression.

re{ n,} Matches n or more occurrences of preceding expression.

re{ n, m} Matches at least n and at most m occurrences of preceding expression.

a| b Matches either a or b.

(re) Groups regular expressions and remembers matched text.

(?: re) Groups regular expressions without remembering matched text.

(?> re) Matches independent pattern without backtracking.

\w Matches word characters.

\W Matches nonword characters.

\s Matches whitespace. Equivalent to [\t\n\r\f].

\S Matches nonwhitespace.

\d Matches digits. Equivalent to [0-9].

\D Matches nondigits.

\A Matches beginning of string.

\Z Matches end of string. If a newline exists, it matches just before newline.

\z Matches end of string.

\G Matches point where last match finished.

\n Back-reference to capture group number "n"

\b Matches word boundaries when outside brackets. Matches backspace (0x08) when inside brackets.

\B Matches nonword boundaries.

\n, \t, etc. Matches newlines, carriage returns, tabs, etc.

\Q Escape (quote) all characters up to \E

\E Ends quoting begun with \Q

Operators
Operators in Java are similar to those in C++.Operators in Java work much like they do in mathematics, producing a value from one or more operands. An operand is any quantity on which an operation can be performed and in Java these include primitives and objects.
Java provides a rich set of operators to manipulate variables. We can divide all the Java operators into the following groups:
* Arithmetic Operators
* Relational Operators
* Bitwise Operators
* Logical Operators
* Assignment Operators
* Misc Operators
The Arithmetic Operators: -
We can use arithmetic operators to perform calculations with values in programs. Arithmetic operators are used in mathematical expressions in the same way that they are used in algebra. A value used on either side of an operator is called an operand. For example, in below statement the expression 47 + 3, the numbers 47 and 3 are operands. The arithmetic operators are examples of binary operators because they require two operands. The operands of the arithmetic operators must be of a numeric type. You cannot use them on boolean types, but you can use them on char types, since the char type in Java is, essentially, a subset of int.
Ex: - int a=47+3;
Assume integer variable A holds 10 and variable B holds 20, then:

Operator Description Example

+ Addition - Adds values on either side of the operator A + B will give 30

- Subtraction - Subtracts right hand operand from left hand operand A - B will give -10

* Multiplication - Multiplies values on either side of the operator A * B will give 200

/ Division - Divides left hand operand by right hand operand B / A will give 2

% Modulus - Divides left hand operand by right hand operand and returns remainder B % A will give 0

++ Increment - Increases the value of operand by 1 B++ gives 21

-- Decrement - Decreases the value of operand by 1 B-- gives 19

public class Test {
public static void main(String args[]) {
int a = 10;
int b = 20;
int c = 25;
int d = 25;
System.out.println("a + b = " + (a + b) );
System.out.println("a - b = " + (a - b) );
System.out.println("a * b = " + (a * b) );
System.out.println("b / a = " + (b / a) );
System.out.println("b % a = " + (b % a) );
System.out.println("c % a = " + (c % a) );
System.out.println("a++ = " + (a++) );
System.out.println("b-- = " + (a--) );
// Check the difference in d++ and ++d
System.out.println("d++ = " + (d++) );
System.out.println("++d = " + (++d) );
}
}
Output: -
a + b = 30
a - b = -10
a * b = 200
b / a = 2
b % a = 0
c % a = 5
a++ = 10
b-- = 11
d++ = 25
++d = 27
The Relational Operators: -
Relational operator compares two values and determines the relationship between them. Relational operators are used to test whether two values are equal, whether one value is greater than another, and so forth.
Assume variable A holds 10 and variable B holds 20, then: -

Operator Description Example

== Checks if the values of two operands are equal or not, if yes then condition becomes true. (A == B) is not true.

!= Checks if the values of two operands are equal or not, if values are not equal then condition becomes true. (A != B) is true.

> Checks if the value of left operand is greater than the value of right operand, if yes then condition becomes true. (A > B) is not true.

< Checks if the value of left operand is less than the value of right operand, if yes then condition becomes true. (A < B) is true.

>= Checks if the value of left operand is greater than or equal to the value of right operand, if yes then condition becomes true. (A >= B) is not true.

<= Checks if the value of left operand is less than or equal to the value of right operand, if yes then condition becomes true. (A <= B) is true.

Example: -
public class Test {
public static void main(String args[]) {
int a = 10;
int b = 20;
System.out.println("a == b = " + (a == b) );
System.out.println("a != b = " + (a != b) );
System.out.println("a > b = " + (a > b) );
System.out.println("a < b = " + (a < b) );
System.out.println("b >= a = " + (b >= a) );
System.out.println("b <= a = " + (b <= a) );
}
}
Output: -
a == b = false
a != b = true
a > b = false
a < b = true
b >= a = true
b <= a = false
Bitwise Operators
The Java programming language also provides operators that perform bitwise and bit shift operations on integral types. The operators discussed in this section are less commonly used. Therefore, their coverage is brief; the intent is to simply make you aware that these operators exist.
The unary bitwise complement operator "~" inverts a bit pattern; it can be applied to any of the integral types, making every "0" a "1" and every "1" a "0". For example, a byte contains 8 bits; applying this operator to a value whose bit pattern is "00000000" would change its pattern to "11111111".
The signed left shift operator "<<" shifts a bit pattern to the left, and the signed right shift operator ">>" shifts a bit pattern to the right. The bit pattern is given by the left-hand operand, and the number of positions to shift by the right-hand operand. The unsigned right shift operator ">>>" shifts a zero into the leftmost position, while the leftmost position after ">>" depends on sign extension.
The bitwise & operator performs a bitwise AND operation.
The bitwise ^ operator performs a bitwise exclusive OR operation.
The bitwise | operator performs a bitwise inclusive OR operation.
Java defines several bitwise operators, which can be applied to the integer types, long, int, short, char, and byte.
Bitwise operator works on bits and performs bit-by-bit operation. Assume if a = 60; and b = 13; now in binary format they will be as follows:
a = 0011 1100
b = 0000 1101
-----------------
a&b = 0000 1100
a|b = 0011 1101
a^b = 0011 0001
~a = 1100 0011
The following table lists the bitwise operators:
Assume integer variable A holds 60 and variable B holds 13 then:

Operator Description Example

& Binary AND Operator copies a bit to the result if it exists in both operands. (A & B) will give 12 which is 0000 1100

| Binary OR Operator copies a bit if it exists in either operand. (A | B) will give 61 which is 0011 1101

^ Binary XOR Operator copies the bit if it is set in one operand but not both. (A ^ B) will give 49 which is 0011 0001

~ Binary Ones Complement Operator is unary and has the effect of 'flipping' bits. (~A ) will give -61 which is 1100 0011 in 2's complement form due to a signed binary number.

<< Binary Left Shift Operator. The left operands value is moved left by the number of bits specified by the right operand. A << 2 will give 240 which is 1111 0000

>> Binary Right Shift Operator. The left operands value is moved right by the number of bits specified by the right operand. A >> 2 will give 15 which is 1111

>>> Shift right zero fill operator. The left operands value is moved right by the number of bits specified by the right operand and shifted values are filled up with zeros. A >>>2 will give 15 which is 0000 1111

Example: -
public class Test {
public static void main(String args[]) {
int a = 60; /* 60 = 0011 1100 */
int b = 13; /* 13 = 0000 1101 */
int c = 0;
c = a & b; /* 12 = 0000 1100 */
System.out.println("a & b = " + c );
c = a | b; /* 61 = 0011 1101 */
System.out.println("a | b = " + c );
c = a ^ b; /* 49 = 0011 0001 */
System.out.println("a ^ b = " + c );
c = ~a; /*-61 = 1100 0011 */
System.out.println("~a = " + c );
c = a << 2; /* 240 = 1111 0000 */
System.out.println("a << 2 = " + c );
c = a >> 2; /* 215 = 1111 */
System.out.println("a >> 2 = " + c );
c = a >>> 2; /* 215 = 0000 1111 */
System.out.println("a >>> 2 = " + c );
}
}
Output: -
a & b = 12
a | b = 61
a ^ b = 49
~a = -61
a << 2 = 240
a >> 15
a >>> 15

operator group	associativity	type of operation
`! ~ ++ -- + -`	right-to-left	unary
`* / %`	left-to-right	multiplicative
`+ -`	left-to-right	additive
`<< >> >>>`	left-to-right	bitwise
`< <= > >=`	left-to-right	comparison
`== !=`	left-to-right	comparison
`&`	left-to-right	bitwise
`^`	left-to-right	bitwise
`\|`	left-to-right	bitwise
`&&`	left-to-right	boolean
`\|\|`	left-to-right	boolean
`?:`	right-to-left	conditional
`= += -= *= /= %= &=` `^= \|= <<= >>= >>>=`	right-to-left	assignment
`,`	left-to-right	comma

Subexpression	Matches
^	Matches beginning of line.
$	Matches end of line.
.	Matches any single character except newline. Using m option allows it to match newline as well.
[...]	Matches any single character in brackets.
[^...]	Matches any single character not in brackets
\A	Beginning of entire string
\z	End of entire string
\Z	End of entire string except allowable final line terminator.
re*	Matches 0 or more occurrences of preceding expression.
re+	Matches 1 or more of the previous thing
re?	Matches 0 or 1 occurrence of preceding expression.
re{ n}	Matches exactly n number of occurrences of preceding expression.
re{ n,}	Matches n or more occurrences of preceding expression.
re{ n, m}	Matches at least n and at most m occurrences of preceding expression.
a\| b	Matches either a or b.
(re)	Groups regular expressions and remembers matched text.
(?: re)	Groups regular expressions without remembering matched text.
(?> re)	Matches independent pattern without backtracking.
\w	Matches word characters.
\W	Matches nonword characters.
\s	Matches whitespace. Equivalent to [\t\n\r\f].
\S	Matches nonwhitespace.
\d	Matches digits. Equivalent to [0-9].
\D	Matches nondigits.
\A	Matches beginning of string.
\Z	Matches end of string. If a newline exists, it matches just before newline.
\z	Matches end of string.
\G	Matches point where last match finished.
\n	Back-reference to capture group number "n"
\b	Matches word boundaries when outside brackets. Matches backspace (0x08) when inside brackets.
\B	Matches nonword boundaries.
\n, \t, etc.	Matches newlines, carriage returns, tabs, etc.
\Q	Escape (quote) all characters up to \E
\E	Ends quoting begun with \Q

Operator	Description	Example
+	Addition - Adds values on either side of the operator	A + B will give 30
-	Subtraction - Subtracts right hand operand from left hand operand	A - B will give -10
*	Multiplication - Multiplies values on either side of the operator	A * B will give 200
/	Division - Divides left hand operand by right hand operand	B / A will give 2
%	Modulus - Divides left hand operand by right hand operand and returns remainder	B % A will give 0
++	Increment - Increases the value of operand by 1	B++ gives 21
--	Decrement - Decreases the value of operand by 1	B-- gives 19

Operator	Description	Example
==	Checks if the values of two operands are equal or not, if yes then condition becomes true.	(A == B) is not true.
!=	Checks if the values of two operands are equal or not, if values are not equal then condition becomes true.	(A != B) is true.
>	Checks if the value of left operand is greater than the value of right operand, if yes then condition becomes true.	(A > B) is not true.
<	Checks if the value of left operand is less than the value of right operand, if yes then condition becomes true.	(A < B) is true.
>=	Checks if the value of left operand is greater than or equal to the value of right operand, if yes then condition becomes true.	(A >= B) is not true.
<=	Checks if the value of left operand is less than or equal to the value of right operand, if yes then condition becomes true.	(A <= B) is true.

Operator	Description	Example
&	Binary AND Operator copies a bit to the result if it exists in both operands.	(A & B) will give 12 which is 0000 1100
\|	Binary OR Operator copies a bit if it exists in either operand.	(A \| B) will give 61 which is 0011 1101
^	Binary XOR Operator copies the bit if it is set in one operand but not both.	(A ^ B) will give 49 which is 0011 0001
~	Binary Ones Complement Operator is unary and has the effect of 'flipping' bits.	(~A ) will give -61 which is 1100 0011 in 2's complement form due to a signed binary number.
<<	Binary Left Shift Operator. The left operands value is moved left by the number of bits specified by the right operand.	A << 2 will give 240 which is 1111 0000
>>	Binary Right Shift Operator. The left operands value is moved right by the number of bits specified by the right operand.	A >> 2 will give 15 which is 1111
>>>	Shift right zero fill operator. The left operands value is moved right by the number of bits specified by the right operand and shifted values are filled up with zeros.	A >>>2 will give 15 which is 0000 1111