A statement performs an action. (In everyday English, a statement is just a sentence that expresses a fact. But in programming languages, that word has a different meaning.) A statement might change the value of a variable or write something, for example. Unlike an expression, a statement does not have an answer. It just does something.
If you write statements one after another then they are performed one after another, in the order in which they are written. For example,
x = 1; y = x + 1;first sets variable x to 1 and then sets variable y to 2.
Java has several places where you must write just one statement. But you often want to write several statements in sequence. In order to do that, wrap the sequence of statements in left and right braces. That yields a compound statement that is treated like a single statement. For example,
{
x = y + 1;
z = w;
}
is a compound statement that, when performed, sets x to
the value of y+1 and then
sets z to the value of w.
A compound statement can contain any number of statements, including none. Statement {} does nothing.