FAQ: Conditional Operators - Combining Conditional Operators

[discourse-admin]

This community-built FAQ covers the “Combining Conditional Operators” exercise from the lesson “Conditional Operators”.

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This exercise can be found in the following Codecademy content:

Build Basic Android Apps with Java

Learn Java

FAQs on the exercise Combining Conditional Operators

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[hampusl]

Never mind, I just got it. I was too busy getting scared off by the math aspect that I forgot to evaluate the statements for what they actually were solving if they are true or false. Followed the order, reminded myself of what && and || actually entails and voila!

[kellyb1019]

Exercise Instructions: Using your understanding of the order of execution, find out whether the value of each expression is true or false .

When you’re ready, uncomment the print statements to find out if you are right.

I am getting stuck here. I have run both sides and the left evaluates to true and the right evaluates to false. true && false evaluates to false but ex1 prints true. what am I missing?

[codebyte]
public class Operators {

public static void main(String args) {

int a = 6;

int b = 3;

boolean ex1 = !(a == 7 && (b >= a || a != a));

// !(a == 7); evaluates true

//b >= a || a != a; evaluates false

System.out.println(ex1);

[codebyte]

[bit1174547489]

I broke it down here that helped me understand ex 1:

int a = 6;

int b = 3;

boolean ex1 = !(a == 7 && (b >= a || a != a));
!(6 == 7 && (3>= 6 || 6 != 6));

Order of operation: parentheses first:

1. (3>= 6 || 6 != 6)
   3>=6 is false
   6 != 6 is false

Now it looks like this:
(false || false)
Answer is false

How our answer looks with the rest:
!(6 == 7 && false);

Order of operation parentheses first:
(6 == 7 && false)

2. 6 ==7 false

Now it looks like:
(false && false) is false

now we have:
!false

our answer is true.

Hope this helps!

[kellyb1019]

Thanks, I sent it to a friend because I couldn’t wait days for a reply! That is the one frustrating thing about codecademy projects. Appreciate you took the time. I hope it helps someone ~

[denny.da.vjncj]

Can anyone provide rationale as to why the highlighted block is evaluating to true?

[arielaDimitria623927]

I’d like to know too

[dev1344639587]

!(b > 3);
is what we focus on first here, according to our order of operations. If we plug in our int value b = 3, we have

!(3 > 3)
we know 3 is not greater than 3, they are equal. expression within parentheses will be false.

!(false)
the ! operator gives us the opposite value of what’s in the parentheses
boolean ex2 = a == b || true;

We know that operand || means OR, so we do not need to evaluate the other portion of the expression. The whole expression is now true.

[profbobo]

Here’s how I worked through the expressions in this exercise. Hopefully it helps.

1. Added a multi-line comment before uncommenting the println() method.
2. Copied and pasted the expression into the comment.
3. On a new line in the comment, replaced the variable names with their values.
4. Worked through the order of execution and replaced the evaluations with their boolean value (on a new line each time).

This helped me visualize what the compiler is doing.
Here is my “work” for the second expression.

boolean ex2 = a == b || !(b > 3);
/*
     a == b || !(b > 3)
     6 == 3 || !(3 > 3)
     6 == 3 || !(false)
     6 == 3 || true
     false || true
     true
*/
// System.out.println(ex2);

true is the answer because || will evaluate to true if either one of the booleans is true.

[board7676274947]

can some one help me understand the code below
boolean ex3 = !(b <= a && b != a + b);
boolean ex2 = a == b || !(b > 3);

[mtrtmk]

The exercise lists the order of precedence for the conditional operators.

For a more complete list of operator precedence, see: https://docs.oracle.com/javase/tutorial/java/nutsandbolts/operators.html

int a = 6;
int b = 3;

boolean ex2 = a == b || !(b > 3);
boolean ex3 = !(b <= a && b != a + b);

// ex2
a == b || !(b > 3)
// Parenthesis has higher precedence.
a == b || !(3 > 3)
a == b || !(false)
a == b || true 
// Equality == has higher precedence than logical OR ||  
// See the operator precedence table in link.
6 == 3 || true
false || true
true 

// ex3
!(b <= a && b != a + b)
// Parentheses has higher precedence.
// Of the operators inside the parentheses, + has the highest precedence
!(b <= a && b != 6 + 3)
!(b <= a && b != 9)
// <= has higher precedence than && and !=
!(3 <= 6 && b != 9)
!(true && b != 9)
// != has higher precedence than &&
!(true && 3 != 9)
!(true && true)
!(true)
false

[board7676274947]

thank you really help full