Conditional Statements and Nested if

if, else if, else

An if statement tests a boolean expression and runs its body only when the expression is true. Chaining with else if builds a decision ladder: Java tests the conditions in order and executes the body of the first one that is true, then skips every remaining branch. A final else runs when no condition matched.

Because the ladder stops at the first match, the conditions in a range ladder must be written from the most restrictive to the least restrictive. A ladder that starts with the widest test can never reach the branches below it, and the compiler reports nothing at all: the code is legal, it simply always answers the same way.

Nested conditionals

An if may appear inside the body of another if. The inner test is reached only when the outer test is true, so a nested pair expresses a logical and. In fact if (p) { if (q) { S } } and if (p && q) { S } behave identically. The two forms stop being interchangeable as soon as either level has an else: an else always belongs to the nearest unmatched if, no matter how the code is indented.