1. Introduction

Expressions, statements, and blocks are the basic components of Java code. They dictate how instructions are written and executed in a program. In this article, we’ll break down these concepts to help you understand their importance in Java programming. More specifically, you learn the different types of Statements and master their differences.

2. Expression

An expression is a structure consisting of variables, operators, and method calls, all arranged according to the programming language syntax, and returning a single value. The data type of the value returned by an expression depends on the data types of the variables used.
Here is an example with the + operator:

valueA + valueB

Another example using the array [] operator:

myArray[index]

An example of a method call:

myObject.toString()

3. Statement

A statement is roughly similar to a sentence in natural language. There are 3 categories of statements in Java: declaration statements, expression statements, and control flow statements.

3.1. Declaration Statement

Java is a strongly typed language, meaning any variable must be declared before its use.
The declaration of a variable obeys the following syntax: dataType variableName
Example:

    int value;

Optionally, you may assign an initialization value:

    int value = 5;

3.2. Expression Statement

An expression statement is an expression that ends with a semicolon (;).
The following are examples of expression statements:

• Assignments : myValue = 10D;
• Increment and decrement operators : i++;, j--;
• Method calls : System.out.println("Learning Java");
• Object creation with the new operator : Student student = new Student();

3.3. Control Flow Statement.

You can read about control flow statements in this dedicated article.

Block

A block is a group of zero or more statements framed by opening ({) and closing (}) curly braces. You can use a block anywhere a single statement is permitted.

        int firstValue = 7;
        int secondValue = 30;
        if(firstValue > secondValue){ // start block 1
            System.out.println("firstValue is greater than secondValue");
        } // end block 1
        else{// start block 2
            System.out.println("fistValue is less than or equal to secondValue");
        }// end block 2

You can nest blocks, meaning that a block may contain another block.

        int firstValue = 7;
        int secondValue = 30;
        int thirdValue = 40;
        if(firstValue > secondValue){ // start block 1
            System.out.println("firstValue is greater than secondValue");
            if(secondValue < thirdValue){// start nested block 2
                System.out.println("secondValue is less than thirdValue");
            }// end nested block 2
        } // end block 1

Please note how the closing brace of the nested block comes before the closing brace of the first block so that the whole forms a well-balanced string of brackets in the sense of the Dyck Language.

4. Conclusion

Congratulations! You now know everything about expressions, statements, and blocks in Java. You are now ready to approach your programs with confidence.

5. References

1) OCP Oracle Certified Professional Java SE 17 by Khalil A. Mughal and Vasily A. Strelnikov
2) Oracle Java Documentation