Expressions, Statements, and Blocks

https://docs.oracle.com/javase/tutorial/java/nutsandbolts/expressions.html
https://www.math.uni-hamburg.de/doc/java/tutorial/java/nutsandbolts/expressions.html


Expression

An expression is a construct made up of variables, operators, and method invocations, which are constructed according to the syntax of the language, that evaluates to a single value. You've already seen examples of expressions, illustrated in bold below:

int cadence = 0;
anArray[0] = 100;
System.out.println("Element 1 at index 0: " + anArray[0]);

int result = 1 + 2; // result is now 3
if (value1 == value2) 
    System.out.println("value1 == value2");

Each expression performs an operation and returns a value, as shown in the following table.

Expression	Action	Value Returned
aChar = 'S'	Assign the character 'S' to the character variable aChar	The value of aChar after the assignment ('S')
"The largest byte value is " + largestByte	Concatenate the string "The largest byte value is " and the value of largestByte converted to a string	The resulting string: The largest byte value is 127
Character.isUpperCase(aChar)	Call the method isUpperCase

compound expression:

 
1 * 2 * 3

x + y / 100    // ambiguous

(x + y) / 100  // unambiguous, recommended

x + (y / 100) // unambiguous, recommended

Statement

A statement forms a complete unit of execution and is terminated with a semicolon (;). There are three kinds of statements: expression statements, declaration statements, and control flow statements.

• Expression Statement:  statement forms a complete unit of execution (expression + ';').

• // assignment statement
  aValue = 8933.234;
  // increment statement
  aValue++;
  // method invocation statement
  System.out.println("Hello World!");
  // object creation statement
  Bicycle myBike = new Bicycle();

• Declaration statement:  declares a variable. 

• double aValue = 8933.234;
  

• 
  
• Control flow statements regulate the order in which statements get executed
• decision-making statements (if-then, if-then-else, switch), 
• the looping statements (for, while, do-while),
• the branching statements (break, continue, return)

Block

A block is a group of zero or more statements between balanced braces and can be used anywhere a single statement is allowed. 

class BlockDemo {
     public static void main(String[] args) {
          boolean condition = true;
          if (condition) { // begin block 1
               System.out.println("Condition is true.");
          } // end block one
          else { // begin block 2
               System.out.println("Condition is false.");
          } // end block 2
     }
}

Quiz:

Operators may be used in building expressions, which compute values.
Expressions are the core components of statements.
Statements may be grouped into blocks.
The following code snippet is an example of a compound expression.

 1 * 2 * 3



Statements are roughly equivalent to sentences in natural languages, but instead of ending with a period, a statement ends with a semicolon.
A block is a group of zero or more statements between balanced braces and can be used anywhere a single statement is allowed.