Java Expressions, Statements and Blocks

In this tutorial, we will learn about Java expressions, Java Statements, and Java blocks with the help of examples.

Java Expressions

A Java expression consists of variables, operators, literals, and method calls.

For example,

int age;
age = 23;

Above, age = 23 is an expression that returns an int.

Let us see the following example,

int x = 12, y = 4, result;
result = x + y  + 10;

Here, x + y + 10 is an expression.

if (num > 10) {
    System.out.println("Number is larger than 10");
}

Here, num > 10 is an expression that returns a boolean value.

Java Statements

In Java, every statement is a complete unit of execution. For example,

int x = 12 + 9;

Here above, we have a statement. The complete execution of this statement involves adding integers 12 and 9 and then assigning the result to the variable x.

Withing the above statement, we have the expression 12 + 9. In Java, expressions are part of statements.

Expression Statements

It is easy to convert an expression into a statement. It consists of terminating the expression with a semicolon ;. For example,

// expression 
a = 17

// statement
a = 17;

Here above, we have the expression a = 17, and just be adding a semicolon ;, we have transformed the expression into a statement a = 17;.

Let us see another example,

// expression 
++i

// statement
++i;

Similarly, ++i is an expression while ++i; is a statement.

Declaration Statements

Declaration statements are used for declaring variables in Java.

Let us consider the following example,

int age = 25;

Here above, the statement declares the variable age that is initialized to 25.

Java Blocks

In Java, a block is a group of statements (zero or more) that are enclosed in curly braces { }.

Example:

public class Main {
    public static void main(String[] args) {
        
        String text = "Hello";

        if (text == "Hello") { // start of the block
            System.out.print("Hello ");
            System.out.println("World");
        } // end of the block 
    }
}

Output

Hello World

Here above, we have a block if { ... }.

Inside the block, we have two statements:

• System.out.print("Hello ");
• System.out.println("World");

In Java, a block may not have any statements. For example,

public class Main {
    public static void main(String[] args) {
        
        int x = 27;

        if (x > 7) { // start of the block

        } // end of the block  
    }
}

Here above, we have a block if { ... } even without any statement inside this block; it is a valid Java program.

Let us see another example,

public class Main {
    public static void main(String[] args) { // start of the block

    } // end of the block 
}

Here above, we have a block public static void main() { ... }, similar to the above example, this block does not have any statement, and it is a valid Java program.