In this unit, we will learn a few more concepts of Java and understand the order of arithmetic calculations.
The values of variables in Java can also be reassigned (modified) as in Python
Example:
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class Main { public static void main(String[] args) { int a = 1; System.out.println(a); a = 2; System.out.println(a); } } |
Output:
1
2
In the above program, the value of the variable a is reassigned to 2
The final keyword is used for variables, classes and methods, which makes them non-changeable (impossible to inherit or override). The final keyword is useful when you want a variable to always store the same value, like PI (3.14159...)
When the final keyword is used with a variable, it indicates that the variable is constant and the value of it cannot be reassigned (cannot be changed)
Example 1:
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class Main { public static void main(String[] args) { final int SPEED_LIMIT = 60; System.out.println(SPEED_LIMIT); } } |
Output:
60
Naming Convention: The naming convention for the final variables is a bit different from normal variables. Generally, programmers follow uppercase letters with words separated by underscore(_). For example, SPEED_LIMIT, MAX_PRICE, etc.
What if the final variable value is changed?
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class Main { public static void main(String[] args) { final int SPEED_LIMIT = 60; SPEED_LIMIT = 90; System.out.println(SPEED_LIMIT); } } |
Output:
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file.java:4: error: cannot assign a value to final variable SPEED_LIMIT SPEED_LIMIT = 90; ^ 1 error |
An error will be thrown. As we learned earlier the value of final variables cannot be changed
An expression is a valid combination of values, variables and operators
Examples:
a * b
a + 2
5 * 2 + 3 / 4
The standard order of evaluating an expression
Brackets (B)
Orders (O)
Division (D)
Multiplication (M)
Addition (A)
Subtraction (S)
Example:
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class Main { public static void main(String[] args) { System.out.println(10 / 2 + 3); System.out.println(10 / (2 + 3)); } } |
Output:
8
2
A statement forms a complete unit of execution. In Java, the expressions can be made into a statement by terminating the expression with a semicolon (;)
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class Main { public static void main(String[] args) { int a = 1; // definition statement System.out.println(a); // method invocation statement } } |
Output:
1
Statement without semicolon (;)
Example
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class Main { public static void main(String[] args) { int a = 1 System.out.println(a); } } |
Output
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file.java:3: error: ';' expected int a = 1 ^ 1 error |
A Block of code consists of zero or more statements enclosed between balanced brackets ({})
Example:
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class Main { // begin block 1 public static void main(String[] args) { // begin block 2 int a = 1; System.out.println(a); } // end block 2 } // end block 1 |
Indentation refers to the spaces at the beginning of a code line. It increases the code readability. In Java, as a best practice, we use four spaces for indentation.
5.2 Missing curly braces ({ or })
Example:
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class Main { public static void main(String[] args) { int a = 1; System.out.println(a); } |
Output:
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file.java:5: error: reached end of file while parsing } ^ 1 error |
In the above program, the closing curly brace } is missing for the Main class (i.e, the braces are not balanced).
In Java, variables can be reassigned.
The final variables cannot be reassigned.
BODMAS: The standard order of evaluating an expression.
In Java, statements are terminated with a semicolon(;).
In Java, a block of code is enclosed between balanced brackets ({})