Difference between revisions of "Java/C2/Logical-Operations/English"

Welcome

Learning Outcomes

how to check for multiple expressions using logical operators and how to overwrite precedence using parentheses

Tools Used

Ubuntu 11.10,

JDK 1.6 and

Eclipse 3.7

Prerequisites

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Logical Operators

Here is a list of the available logical operators in Java

Switch to Eclipse.

Eclipse should contain the following code

public class LogicalOperators{

public static void main(String[] args){

}

}

We have created a class LogicalOperators and added the main method

Let us create some variables.

int age = 11;

int weight = 42;

We shall store the result of conditions in b;

 int age is equalto 11   

int weight isequalto 42

int age = 11;

int weight = 42;

We shall check if the person is below 18yrs of age and is atleast 40kgs.

Let us see how to do so.

boolean b;

b = age < 18 && weight >= 40

Highlight &&

Highlight expression

b is eual toage less than 18 ampersand ampersand weight greater than equal to 40

This statement has two expressions and a double ampersand symbol in between.

It checks if age is less than 18 and also if weight is greater than or equal to 40.

This operation is called the and operation.

System.out.println();

System dot out dot println(b);

Change 42 to 32.

Save and Run.

Now let us change the weight so that one condition is not satisfied and re run the code.

Change 42 to 32.

Save and Run

This is because the condition age less than 18 is satisfied

But the condition the weight is greater than or equal to 40 is not satisfied

The and operation requires both the conditions to be true for the result to be true.

Therefore we get false as our output.

In other words, we need to see if the first condition or the second condition is true.

It is done using the or operation.

b = age <= 15 || weight <= 30

Type

age less than equal to 15 pipe pipe weight less than equal to 30

There are two conditions and a double pipe symbol in between.

This statement checks if atleast one of the given two conditions is satisfied.

Let us run the code to see the output.

Save and Run.

Point to output

Save and Run

Now the output is false because both the conditions are not satisfied.

In other words, we need to check the exact opposite of the condition we just did.

age... line

As we can see, the output is the opposite of earlier one.

Or people younger than 18 and lighter than 40kilos.

Let us see how would we go about this condition.

age < 15 || age < 18 && weight < 40

Highlight the condition.

age less than 15

or age less than 18

and weight less than 40

As we can see, the condition itself is confusing.

Moreover, we do not know if the or operation will be performed first or the and operation.

It depends on the precedence of operators.

In such situations, we use parentheses to overwrite the precedence and also make the condition clear.

to (age <= 18 && weight <= 40)

Save. Run.

the second condition, which is,

age less than 18 and weight less than 40 is satisfied.

Therefore, output is True.

Slide 6

Summary

In this tutorial we have learnt about logical operators, how to check for multiple expressions using logical operators and

how to override the precedence using parentheses.

find out if the two expressions, shown are equivalent?

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