4.Lesson Plan - Java Operators.pdf...pdf

Cracking the Coding Interview in JAVA - Foundation
Pre-Requisites:
List of Concepts Involved:
Topic 1: Java Operators
1.Java Arithmetic operators:
Java Basic syntax for input and output
Data types
Variables
Identifiers
Keywords
Operators
Operators precedence and associativity.
Operators are the symbols that are used to perform pre-defined operations on variables and values
(commonly referred to as operands). As soon as the compiler encounters an operator, it performs the specific
mathematical or logical operation and returns the result.

Let us learn and understand about the relevant operators in detail.

Operators in Java can be classified into 6 types:
Arithmetic Operators
Relational Operators
Logical Operators
Assignment Operators
Unary Operators
Bitwise Operators
Arithmetic operators are used in mathematical expressions in a program. They function in the same way as
they do in algebra.

The following table lists the arithmetic operators:

Assume integer variable num1 holds a value of 20, variable num2 holds a value of 30 and num3 holds a value
of 30, then:

Let us now write a simple program to implement all the operators.You may try it yourself too !

Example:

class Main {

public static void main(String[] args) {

int p = 20, q = 10;

int result;

result=p+q;

System.out.println(result);

System.out.println(p - q);

System.out.println(p * q);

System.out.println(p / q);

System.out.println(p % q);

}

}
// declare variables p and q
// addition operator
// subtraction operator
// we can directly perform subtraction in print statement,no need

// to use result variable here

// multiplication operator
// division operator

// modulo operator

2.Java Relational Operators:
Output

30

10

200

2

0
Relational operators compare numeric, character string, or logical data. The result of the comparison, either
true ( 1 ) or false ( 0 ), can be used to make a decision regarding program flow. The table below enlists
relational operators used in Java.
Let us write a program to implement all of these.

class Main {


int p = 10, q = 15;

System.out.println(p == q); // false

System.out.println(p != q); // true

System.out.println(p > q); // false

System.out.println(p < q); // true

System.out.println(p >= q); // false

System.out.println(p <= q); // true

}

}
// create variables

// == operator

// != operator

// > operator

// < operator

// >= operator

// <= operator

3.Java Logical Operators
Output

false

true

false

true

false

true
Logical operators are used for decision making. This class of operators is used to check whether an expression
is true or false. Some of the commonly used logical operators are mentioned in the table below.
Let us look at the following program to understand it better.

Example code:

class Main {


int p=15,q=10,r=5;

System.out.println((p > q) && (p > r)); // true

System.out.println((p > q) && (p < r)); // false

System.out.println((r < q) || (p < q)); // true

System.out.println((p > q) || (q > r)); // true

System.out.println((p < q) || (p < r)); // false

System.out.println(!(p == q)); // true

System.out.println(!(p > q)); // false

}

}

Output:

true

false

true

true

false

true

false
// && operator
// || operator
// ! operator

4.Java assignment operators:
The assignment operator = assigns the value of its right-hand operand to a variable, a property, or an indexer
element given by its left-hand operand. Confused? Don’t worry, we have you covered here.

Let's have a look at some of the commonly used assignment operators available in Java with examples.
Try out the following example for better understanding.

Example code:

class Main {


int p = 10;

int q;

q = p;

System.out.println(q); // value of q is 10

q += p;


q *= p;


}

}

Output:

10

20

200
// assign value using =

// assign value using =+

// assign value using =*

5.Java Unary Operators:
Question: Is there any performance difference between x+=y and x=x+y?

Solution: Yes, x+=y performs better than x=x+y.

Eg. x += 10 means
Find the place identified by x
Add 10 to it

And x = x + 10 means
Evaluate x+10
Find the place(memory) identified by the variable x
Copy x into an accumulator (accumulator is a part of CPU for temporary storage)
Add 10 to the accumulator
Store the result in variable x
Find the place (memory) identified by x
Copy the accumulator(result) to it

Hence, clearly x=+10 is better than x=x+10 since evaluation is direct with no intermediate steps for CPU to
perform.

Let us look at the next class of operators.
Interestingly, unlike the normal operators seen so far, java unary operators need only one operand to perform
operations like increment, decrement, negation, etc.

The table below will help you understand it in a better way.
For example:

class Main {


int p = 5;

System.out.println("Post-Increment Operator");

System.out.println(p++); // 5

// initialize p
// / p's value is incremented to 6 after returning current value i.e; 5

6.Java Bitwise operators:
int q = 5;

System.out.println("Pre-Increment Operator");

System.out.println(++q); //6

}

}

Output:

Post-Increment Operator

5

Pre-Increment Operator

6
// initialized to 5

// q is incremented to 6 and then it's value is returned
Interestingly, unlike the normal operators seen so far, java unary operators need only one operand to perform
operations like increment, decrement, negation, etc.

The table below will help you understand it in a better way.
Let's look at a simple code to understand the working of these operators.

Example code:

class Main {


int p = 5;

System.out.println(p<<2);

}

}
// initialize p

// Shifting the value of p towards the left two positions

Output 20

Explanation:

Shifting the value of p towards the left (two positions) will make the leftmost 2 bits to be lost. The value of p is 5.
The binary representation of 5 is 00000101(we will learn about this conversion in the forthcoming lecture).

After 2 left shifts, binary representation of p will be 00010100 which is equivalent to 20.

Now that we have learnt about all types of operators, its a good time to explore the precedence/priority of each
of these wrt each other in different scenarios.
Topic : Java Operator Precedence and Associativity
Operator precedence determines the order/sequence of evaluation of operators in an expression (analogous
to BODMAS concept in maths).

Take a look at the statement below:

int ans = 10 - 4 * 2;

What will be the value of variable ans? Will it be (10 - 4)*2, that is, 12? Or it will be 10 - (4 * 2), that is, 2?

When two operators share a common operand (4 in this case), the operator with the highest precedence is
operated upon first. In java, the precedence of * is higher than that of -. Hence, multiplication is performed
before subtraction, and hence the final value of the variable ans will be 2.

Associativity of Operators in Java

A question arises here, what if the precedence of all operators in an expression is same? In that case, the
concept of associativity comes into picture.

Associativity specifies the order in which operators are evaluated by the compiler, which can be left to right or
right to left. For example, in the phrase p = q = r = 10, the assignment operator is used from right to left. It means
that the value 10 is assigned to r, then r is assigned to q, and at last, q is assigned to p. This phrase can be
parenthesized as (p = (q = (r = 10))).

Operator Precedence in Java (Highest to Lowest)
Let us try a few questions on precedence and associativity to clear the air of confusion.

Example 1.

Let say we have 4 variables of type int ; p,q,r,s

s = p-++r-++q;

is equivalent to

Answer: s = p-(++r)-(++q);

Explanation: The operator precedence of prefix ++ is higher than that of - subtraction operator.

Example 2. What does the following code fragment print?

System.out.println(4 + 2 + "pqr");

System.out.println("pqr" + 4 + 2);

Answer: 6pqr and pqr42, respectively.

Explanation: The + operator is left-to-right associative, whether it is string concatenation or simple number
addition.

Example 3: What is the result of the following code fragment? Explain.

boolean p = false;

boolean q = false;

boolean r = true;

System.out.println(p == q == r);

Answer: It prints true.

Explanation: The equality operator is left-to-right associative, so p == q evaluates to true and this result is
compared to r, which yields true.

This brings us to the end of the lecture !

Keep Learning ! Keep Exploring !!
Upcoming Class Teaser
Java conditionals
if/else
switch

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