#18 Known is a Drop! Conditional Statement-if--else in JAVA

#beginners #java #programming #tutorial

1. What is an if-else statement?
It is a decision-making statement used to execute code based on a condition (true/false).
2. What is the syntax of if-else?

if (condition) {
    // executes if true
} else {
    // executes if false
}

3. Can we use if without else?
Yes, else is optional.

4. Difference between if-else and switch?
if-else → works with ranges, conditions
switch → works with fixed values (int, String, enum)

5. What is an else if ladder?
if (marks > 90) {
System.out.println("A");
} else if (marks > 75) {
System.out.println("B");
} else {
System.out.println("C");
}

6.What is nested if?

if (age > 18) {
if (hasLicense) {
System.out.println("Can drive");
}
}
7. What happens if you miss curly braces {}?

if (true)
System.out.println("Hello");
System.out.println("World");
Output:
Hello
World
8. Can we write multiple conditions in if?
Yes
if (age > 18 && country.equals("USA")) {
System.out.println("Eligible");
}

9. What is the ternary operator (shortcut for if-else)?
int result = (a > b) ? a : b;

10.Can if condition be non-boolean in Java?
❌ No — must return boolean (true/false)

11.What will this output?
int x = 10;
if (x = 5) {
System.out.println("Hello");
}
❌ Compile-time error (condition must be boolean)
= is assignment not relational operator like ==

12.Floating Point Comparison Trap
Version1
double a = 0.1 + 0.2;

if (a == 0.3) {
System.out.println("Equal");
} else {
System.out.println("Not Equal");
}
Output:
Not Equal
value of a is value of a 0.30000000000000004
Due to precision issues in floating-point arithmetic
Version2:


package module3;

public class Sample {
    public static void main(String[] args) {
        float a = 0.1f + 0.2f;
        System.out.println("value of a  " + a);
System.out.printf("To print the actual value of a in memory with 10 precision values is %.10f ", a);
        System.out.println();
        if (a == 0.3) {
            System.out.println("Equal");
        } else {
        System.out.println("Not Equal  " + a);
        }

    }

}

output:
value of a 0.3
To print the actual value of a in memory with 10 precision values is 0.3000000119
Not Equal 0.3
Behind the scenes:
Why does System.out.println(a) show 0.3?

System.out.println() uses formatted output, not raw memory value.
It converts the float to a string
While converting, it rounds to a reasonable number of digits
So small precision errors are hidden.
Memory value ≠ Printed value
Java rounds for readability
Comparison (==) uses actual value, not printed value

13.OR (||) Short Circuit
int a = 5;

if (a < 10 || ++a < 20) {
System.out.println(a);
}
Behind the scene:
First condition is true → second NOT executed
Output: 5

14.AND (&&) Short Circuit

int a = 5;

if (a > 10 && ++a < 20) {
    System.out.println(a);
}

System.out.println(a);

Answer:
First condition is false → second is NOT executed
Output: 5

Tips:What is short-circuit evaluation?

In &&, if first condition is false → second is NOT checked
In ||, if first condition is true → second is NOT checked

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#18 Known is a Drop! Conditional Statement-if--else in JAVA

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