Boolean Expressions

int x = 10;

x > 5          // true
x == 10        // true
x != 10        // false
x < 0          // false
x >= 10        // true
x <= 9         // false

int temperature = 95;

if (temperature > 90) {
    System.out.println("It's hot outside!");
}
// Output: It's hot outside!

int temperature = 72;

if (temperature > 90) {
    System.out.println("It's hot outside!");   // skipped
}
// No output

if (condition) {      // condition must be a boolean expression
    // code to run    // only runs if condition is true
}                     // curly braces define the block

int score = 95;

if (score >= 90) {
    System.out.println("A");       // prints
}
if (score >= 80) {
    System.out.println("B");       // ALSO prints!
}
if (score >= 70) {
    System.out.println("C");       // ALSO prints!
}
// Output: A B C (all three!)

if (true) {
    int x = 10;          // x exists only here
    System.out.println(x); // works
}
// System.out.println(x);  // COMPILE ERROR — x doesn't exist here

int x = 10;
if (x > 5) {
    x = 20;              // modifying x from outer scope — works
}
System.out.println(x);    // 20

// Legal but dangerous:
if (x > 0)
    System.out.println("positive");

// TRAP — this is NOT part of the if:
if (x > 0)
    System.out.println("positive");
    System.out.println("done");     // ALWAYS runs! (not inside the if)

int a = 15;
int b = 20;
int c = 15;

if (a == c) {
    System.out.print("X");
}
if (a > b) {
    System.out.print("Y");
}
if (b > a) {
    System.out.print("Z");
}