Expressions versus statements

Expressions.java

public class Expressions {

    public static void main(String[] args) {
        // Expressions evaluate to a value...
        int z = 1 + 1;
        //      ^^^^^

        // Statements do not. 
        System.out.println("This is a statement.");
        
        // Assignments are statements
        z = 2;

        // .. but can contain expressions
        z = 2 * z;
        
        // Statements may contain expressions.. or they may not. (like the println above)
        // An expressionless statement is only called for its 'side-effect'. 
        // (In this case, side-effect == printing)

        // Expressions can be compound and parenthesized
        z = (z + (z * 2))) * z;

        // Statements cannot be compound (illegal)
        // (x++)(y++);
        
        // In the simple case, expressions cannot be on a line by themselves. (illegal)
        // z + z + 1

        // Statements are terminated by a semi-colon
        z++;

        // A block is a group of zero or more statements
        // They can be used anywhere a single statement is allowed
        {
            System.out.println("This belongs to the block.");
            System.out.println("So does this. " + z);
        }
    }
}