- You guessed it:
- The ++ and -- are operators that return a value
- Pre- and post operators:
- There are two versions
of the ++ and
the -- operators:
- Pre-operation: the
++ and -- operator appear
before the variable
++var pre-increment operator --var pre-decrement operator
- Post-operation: the
++ and -- operator appear
after the variable
var++ post-increment operator var-- post-decrement operator
- Pre-operation: the
++ and -- operator appear
before the variable
- There are two versions
of the ++ and
the -- operators:
- Difference between a
++var and
var++:
- Both operations
(++var and
var++)
will
increment the
variable var
by 1
(so no different here)
- The only difference between
++var and
var++ is:
- the value that is returned by the expression.
The above also apply for --var and var--.
(Except that that instead of incrementing the variable var by 1, the -- operators will decrement by 1)
- Both operations
(++var and
var++)
will
increment the
variable var
by 1
(so no different here)
- Result returned by the
++ and
-- operators:
Value in a Operation Value in a
after operationReturned value 4 ++a 5 5 4 a++ 5 4 4 --a 3 3 4 a-- 3 4 In other words:
- The pre-operations
++a and
--a will:
- Apply the increment/decrement operation before (pre) returning the value in the variable a
- The post-operations
a++ and
a-- will:
- Apply the
increment/decrement operation
after (post)
returning the
value in the variable a
(The computer will saved the orignal value of the variable a, perform the operation and then returned the saved value)
- Apply the
increment/decrement operation
after (post)
returning the
value in the variable a
- The pre-operations
++a and
--a will:
- Example:
public class Increment01 { public static void main(String[] args) { int a; a = 4; System.out.println(++a); // Prints 5 System.out.println(a); // Prints 5 a = 4; System.out.println(a++); // Prints 4 System.out.println(a); // Prints 5 a = 4; System.out.println(--a); // Prints 3 System.out.println(a); // Prints 3 a = 4; System.out.println(a--); // Prints 4 System.out.println(a); // Prints 3 } }
- Example Program:
(Try it out for yourself...)
- Prog file: click here
How to run the program:
- Right click on link and
save in a scratch directory
- To compile: javac Increment01.java
- To run: java Increment01
- Priority of the
++
and -- operators:
- The ++ and
-- operators are
unary operators
Their priority ranks at he same level as other unary operators (such as the negation operator)
- In most cases (because you would rarely use
++ and -- mixed with other operators), you only need to
remember that:
- The ++ and -- operators have higher priority than any binary arithmetic operators in Java
- The ++ and
-- operators are
unary operators
- Example:
public class AssignExpr05 { public static void main(String[] args) { int a, b; a = 4; b = ++a + 1; // ++a evaluates to 5, so: 5 + 1 = 6 System.out.println(a); // Prints 5 System.out.println(b); // Prints 6 a = 4; b = a++ + 1; // a++ evaluates to 4, so: 4 + 1 = 5 System.out.println(a); // Prints 5 System.out.println(b); // Prints 5 } }Explanation:
b = ++a + 1; is evaluated as follows: b = ++a + 1; higher priority ^^^ ++a evaluates to 5 Reduces to: b = 5 + 1; = 6;
b = a++ + 1; is evaluated as follows: b = a++ + 1; higher priority ^^^ ++a evaluates to 4 Reduces to: b = 4 + 1; = 5;
- Example Program:
(Try it out yourself)
- Prog file: click here
How to run the program:
- Right click on link and
save in a scratch directory
- To compile: javac AssignExpr05.java
- To run: java AssignExpr05
- What will the following Java program
print:
public class AssignExpr06 { public static void main(String[] args) { int a, b; a = 4; b = 2 * --a + 1; System.out.println(a); System.out.println(b); a = 4; b = 2 * (a-- + 1); System.out.println(a); System.out.println(b); } }Answer:
3 7 3 10
- Example Program:
(Verify for yourself...)
- Prog file: click here
How to run the program:
- Right click on link and
save in a scratch directory
- To compile: javac AssignExpr06.java
- To run: java AssignExpr06
- The following expressions
are syntactically incorrect:
a ++ -- or ++ -- a
Error: unexpected type required: variable found : value a ++ --; ^ Why it is syntactically incorrect: a ++ -- ===> (a ++) -- -- needs to operate on a variable ^^^^^^ is a valueBecause we don't encounter these constructs, I will omit the discussion of the associativity rules of the ++ and -- operators.
- I can refer you to a website with the information: click here