Операторы if

Running code conditionally

• An if statement 条件语句 runs a block only when its condition is true.
• if (score >= 60) { System.out.println("Pass"); }
• If the condition is false, the block is skipped entirely.
• This is selection — the program chooses whether to run the block.

Adding else

• An else clause runs alternative code when the condition is false.
• if (score >= 60) { print("Pass"); } else { print("Fail"); }
• Exactly one of the two branches runs — never both, never neither.
• else is optional; a bare if just skips its block when false.

Traffic lights: selection chooses which branch runs, just as if statements choose code paths

Braces group the block

• Braces { } group the statements that belong to the if or else.
• Without braces, only the single next statement is controlled by the if.
• Always use braces, even for one line — it prevents a common bug.
• Indent the block so the structure is visible at a glance.

Tracing the branch

• To trace an if-else, evaluate the condition, then run the matching branch.
• With score = 75: 75 >= 60 is true → run the if block → prints "Pass".
• With score = 40: 40 >= 60 is false → run the else block → prints "Fail".
• Only the code in the chosen branch executes.