Friday, 27 February 2015

Summary of Operators in Java



The following quick reference summarizes the operators supported by the Java programming language.

Simple Assignment Operator

= Simple assignment operator

Arithmetic Operators

+ Additive operator (also used for String concatenation)
- Subtraction operator
* Multiplication operator
/ Division operator
% Remainder operator

Unary Operators

+ Unary plus operator; indicates positive value (numbers are positive without this, however)
- Unary minus operator; negates an expression
++ Increment operator; increments a value by 1
-- Decrement operator; decrements a value by 1
! Logical complement operator; inverts the value of a boolean

Equality and Relational Operators

== Equal to
!= Not equal to
> Greater than
>= Greater than or equal to
< Less than
<= Less than or equal to

Conditional Operators

&& Conditional-AND
|| Conditional-OR
?: Ternary (shorthand for if-then-else statement)

Type Comparison Operator

instanceof Compares an object to a specified type

Bitwise and Bit Shift Operators

~ Unary bitwise complement
<< Signed left shift
>> Signed right shift
>>> Unsigned right shift
& Bitwise AND
^ Bitwise exclusive OR
| Bitwise inclusive OR

Precedence of Java Operators:

Operator precedence determines the grouping of terms in an expression. This affects how an expression is evaluated. Certain operators have higher precedence than others; for example, the multiplication operator has higher precedence than the addition operator:
For example, x = 7 + 3 * 2; here x is assigned 13, not 20 because operator * has higher precedence than +, so it first gets multiplied with 3*2 and then adds into 7.
Here, operators with the highest precedence appear at the top of the table, those with the lowest appear at the bottom. Within an expression, higher precedence operators will be evaluated first.
CategoryOperatorAssociativity
Postfix () [] . (dot operator)Left toright 
Unary ++ - - ! ~Right to left 
Multiplicative  * / % Left to right 
Additive  + - Left to right 
Shift  >> >>> <<  Left to right 
Relational  > >= < <=  Left to right 
Equality  == != Left to right 
Bitwise AND Left to right 
Bitwise XOR Left to right 
Bitwise OR Left to right 
Logical AND && Left to right 
Logical OR || Left to right 
Conditional ?: Right to left 
Assignment = += -= *= /= %= >>= <<= &= ^= |= Right to left 
Comma Left to right 

Questions and Exercises: Operators


Questions

  1. Consider the following code snippet.
    arrayOfInts[j] > arrayOfInts[j+1]
    Which operators does the code contain?
  2. Consider the following code snippet.
    int i = 10;
    int n = i++%5;
    1. What are the values of i and n after the code is executed?
    2. What are the final values of i and n if instead of using the postfix increment operator (i++), you use the prefix version (++i))?
  3. To invert the value of a boolean, which operator would you use?
  4. Which operator is used to compare two values, = or == ?
  5. Explain the following code sample: result = someCondition ? value1 : value2;

Exercises

  1. Change the following program to use compound assignments:
    class ArithmeticDemo {

    public static void main (String[] args){

    int result = 1 + 2; // result is now 3
    System.out.println(result);

    result = result - 1; // result is now 2
    System.out.println(result);

    result = result * 2; // result is now 4
    System.out.println(result);

    result = result / 2; // result is now 2
    System.out.println(result);

    result = result + 8; // result is now 10
    result = result % 7; // result is now 3
    System.out.println(result);
    }
    }

  2. In the following program, explain why the value "6" is printed twice in a row:
    class PrePostDemo {
    public static void main(String[] args){
    int i = 3;
    i++;
    System.out.println(i); // "4"
    ++i;
    System.out.println(i); // "5"
    System.out.println(++i); // "6"
    System.out.println(i++); // "6"
    System.out.println(i); // "7"
    }
    }

Saturday, 7 February 2015

Equality, Relational, and Conditional Operators


The Equality and Relational Operators

The equality and relational operators determine if one operand is greater than, less than, equal to, or not equal to another operand. The majority of these operators will probably look familiar to you as well. Keep in mind that you must use "==", not "=", when testing if two primitive values are equal.
==      equal to
!= not equal to
> greater than
>= greater than or equal to
< less than
<= less than or equal to
The following program, ComparisonDemo, tests the comparison operators:
class ComparisonDemo {

public static void main(String[] args){
int value1 = 1;
int value2 = 2;
if(value1 == value2)
System.out.println("value1 == value2");
if(value1 != value2)
System.out.println("value1 != value2");
if(value1 > value2)
System.out.println("value1 > value2");
if(value1 < value2)
System.out.println("value1 < value2");
if(value1 <= value2)
System.out.println("value1 <= value2");
}
}
Output:
value1 != value2
value1 < value2
value1 <= value2

The Conditional Operators

The && and || operators perform Conditional-AND and Conditional-OR operations on two boolean expressions. These operators exhibit "short-circuiting" behavior, which means that the second operand is evaluated only if needed.
&& Conditional-AND
|| Conditional-OR
The following program, ConditionalDemo1, tests these operators:
class ConditionalDemo1 {

public static void main(String[] args){
int value1 = 1;
int value2 = 2;
if((value1 == 1) && (value2 == 2))
System.out.println("value1 is 1 AND value2 is 2");
if((value1 == 1) || (value2 == 1))
System.out.println("value1 is 1 OR value2 is 1");
}
}
Another conditional operator is ?:, which can be thought of as shorthand for an if-then-else statement (discussed in the Control Flow Statements section of this lesson). This operator is also known as the ternary operator because it uses three operands. In the following example, this operator should be read as: "If someCondition is true, assign the value of value1 toresult. Otherwise, assign the value of value2 to result."
The following program, ConditionalDemo2, tests the ?: operator:
class ConditionalDemo2 {

public static void main(String[] args){
int value1 = 1;
int value2 = 2;
int result;
boolean someCondition = true;
result = someCondition ? value1 : value2;

System.out.println(result);
}
}
Because someCondition is true, this program prints "1" to the screen. Use the ?: operator instead of an if-then-else statement if it makes your code more readable; for example, when the expressions are compact and without side-effects (such as assignments).

The Type Comparison Operator instanceof

The instanceof operator compares an object to a specified type. You can use it to test if an object is an instance of a class, an instance of a subclass, or an instance of a class that implements a particular interface.
The following program, InstanceofDemo, defines a parent class (named Parent), a simple interface (named MyInterface), and a child class (named Child) that inherits from the parent and implements the interface.
class InstanceofDemo {
public static void main(String[] args) {

Parent obj1 = new Parent();
Parent obj2 = new Child();

System.out.println("obj1 instanceof Parent: "
+ (obj1 instanceof Parent));
System.out.println("obj1 instanceof Child: "
+ (obj1 instanceof Child));
System.out.println("obj1 instanceof MyInterface: "
+ (obj1 instanceof MyInterface));
System.out.println("obj2 instanceof Parent: "
+ (obj2 instanceof Parent));
System.out.println("obj2 instanceof Child: "
+ (obj2 instanceof Child));
System.out.println("obj2 instanceof MyInterface: "
+ (obj2 instanceof MyInterface));
}
}

class Parent {}
class Child extends Parent implements MyInterface {}
interface MyInterface {}
Output:
obj1 instanceof Parent: true
obj1 instanceof Child: false
obj1 instanceof MyInterface: false
obj2 instanceof Parent: true
obj2 instanceof Child: true
obj2 instanceof MyInterface: true
When using the instanceof operator, keep in mind that null is not an instance of anything.

Thursday, 5 February 2015

Operator


Java provides a rich set of operators to manipulate variables. We can divide all the Java operators into the following groups:
Arithmetic operators are used in mathematical expressions in the same way that they are used in algebra. The following table lists the arithmetic operators :
Assume integer variable A holds 10 and variable B holds 20, then:
SR.NO Operator and Example
1+ ( Addition )
Adds values on either side of the operator
Example: A + B will give 30
2- ( Subtraction )
Subtracts right hand operand from left hand operand
Example: A - B will give -10
3* ( Multiplication )
Multiplies values on either side of the operator
Example: A * B will give 200
4/ (Division)
Divides left hand operand by right hand operand
Example: B / A will give 2
5% (Modulus)
Divides left hand operand by right hand operand and returns remainder
Example: B % A will give 0
6++ (Increment)
Increases the value of operand by 1
Example: B++ gives 21
7-- ( Decrement )
Decreases the value of operand by 1
Example: B-- gives 19
There are following relational operators supported by Java language
Assume variable A holds 10 and variable B holds 20, then:
SR.NO Operator and Example
1== (equal to)
Checks if the values of two operands are equal or not, if yes then condition becomes true.
Example: (A == B) is not true.
2!= (not equal to)
Checks if the values of two operands are equal or not, if values are not equal then condition becomes true.
Example: (A != B) is true.
3> (greater than)
Checks if the value of left operand is greater than the value of right operand, if yes then condition becomes true.
Example: (A > B) is not true.
4< (less than)
Checks if the value of left operand is less than the value of right operand, if yes then condition becomes true.
Example: (A < B) is true.
5>= (greater than or equal to)
Checks if the value of left operand is greater than or equal to the value of right operand, if yes then condition becomes true.
Example (A >= B) is not true.
6<= (less than or equal to)
Checks if the value of left operand is less than or equal to the value of right operand, if yes then condition becomes true.
example(A <= B) is true.
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 :

SR.NO Operator and Description
1& (bitwise and)
Binary AND Operator copies a bit to the result if it exists in both operands.
Example: (A & B) will give 12 which is 0000 1100
2| (bitwise or)
Binary OR Operator copies a bit if it exists in either operand.
Example: (A | B) will give 61 which is 0011 1101
3^ (bitwise XOR)
Binary XOR Operator copies the bit if it is set in one operand but not both.
Example: (A ^ B) will give 49 which is 0011 0001
4~ (bitwise compliment)
Binary Ones Complement Operator is unary and has the effect of 'flipping' bits.
Example: (~A ) will give -61 which is 1100 0011 in 2's complement form due to a signed binary number.
5<< (left shift)
Binary Left Shift Operator. The left operands value is moved left by the number of bits specified by the right operand
Example: A << 2 will give 240 which is 1111 0000
6>> (right shift)
Binary Right Shift Operator. The left operands value is moved right by the number of bits specified by the right operand.
Example: A >> 2 will give 15 which is 1111
7>>> (zero fill right shift)
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.
Example: A >>>2 will give 15 which is 0000 1111
The following table lists the logical operators :
Assume Boolean variables A holds true and variable B holds false, then :

SR.NO Operator and Description
1&& (logical and)
Called Logical AND operator. If both the operands are non-zero, then the condition becomes true.
Example (A && B) is false.
2|| (logical or)
Called Logical OR Operator. If any of the two operands are non-zero, then the condition becomes true.
Example (A || B) is true.
3! (logical not)
Called Logical NOT Operator. Use to reverses the logical state of its operand. If a condition is true then Logical NOT operator will make false.
Example !(A && B) is true.
There are following assignment operators supported by Java language :
SR.NO Operator and Description
1=
Simple assignment operator, Assigns values from right side operands to left side operand.
Example: C = A + B will assign value of A + B into C
2+=
Add AND assignment operator, It adds right operand to the left operand and assign the result to left operand.
Example: C += A is equivalent to C = C + A
3-=
Subtract AND assignment operator, It subtracts right operand from the left operand and assign the result to left operand.
Example:C -= A is equivalent to C = C - A
4*=
Multiply AND assignment operator, It multiplies right operand with the left operand and assign the result to left operand.
Example: C *= A is equivalent to C = C * A
5/=
Divide AND assignment operator, It divides left operand with the right operand and assign the result to left operand
ExampleC /= A is equivalent to C = C / A
6%=
Modulus AND assignment operator, It takes modulus using two operands and assign the result to left operand.
Example: C %= A is equivalent to C = C % A
7<<=
Left shift AND assignment operator.
ExampleC <<= 2 is same as C = C << 2
8>>=
Right shift AND assignment operator
Example C >>= 2 is same as C = C >> 2
9&=
Bitwise AND assignment operator.
Example: C &= 2 is same as C = C & 2
10^=
bitwise exclusive OR and assignment operator.
Example: C ^= 2 is same as C = C ^ 2
11|=
bitwise inclusive OR and assignment operator.
Example: C |= 2 is same as C = C | 2