java basic

Last update:2018-05-08

This is the second section of part 1.

Operator is a kind of signs which has certain function,in order to notify Java to do certain operations.

There are several common operators down below that you can see in Java:

Arithmetic operators

Arithmetic operators mainly are use to do basic arithmetic operations,such as addition,subtraction, mutiplication and division etc.

Common arithmetic operators in Java:

Arithmetic operators	Definition	Example
+	Addition	5 + 12 = 17
-	Subtraction	25 - 10 = 15
*	Multiplication	3 * 8 = 24
/	Division	24 / 6 = 4
%	Modulus	24 % 7 = 3
++	Increment	int i = 5;i++
–	decrement	int i = 5;i–

Notice:

There are some differences between modulo operation and remainder operation,% means remainder in C/C++ and Java,but modulo in Python.
++/– can be on the left side or the right side of the number,but the output is different

Ex.1

//Left side
int a = 5;
int b = ++a;//Variable a wil execute increment first,and then assign the value to variable b
System.out.println("a:" + a);
System.out println("b:" + b);

Output

1
2

a:6
b:6

Ex.2

//Right side
int a = 5;
int b = ++a;//Variable a's value will be assign to variable b fisrt,and then execute increment
System.out.println("a:" + a);
System.out println("b:" + b);

Output

1
2

a:6
b:5

Both increment operator and decrement operator can only use to operate variables,you can’t directly on values or constants.

1 2	5++;//Wrong 8--;//Wrong

Assignment operators

Assignment operators is a kind of notation that use to assign value for variables and constants

Common assignment operators in Java:

Operator	Definition	Example
=	Assignment	c = a + b,assign the sum of a & b to c
+=	Addition	a += b,assign the sum of a & b to a
-=	Subtraction	a -= b,assign the margin of a - b to a
*=	Multiplication	a *= b,assign the product of a & b to a
/=	Division	a /= b,assign the quotient of a & b to a
%=	Modulus	a %= b,assign the remainder of a divide by b to a

Comparison operators

Comparsion operators is use to compare two values,and output a boolean value(true or false)

Common comparsion operators in Java:

Operator	Definition	Example	Output
>	Greater than	a = 5;b = 2;a > b	true
<	Less than	a = 5;b = 2;a < b	false
>=	Greater or equal	a = 5;a >= 3	true
<=	Less or equal	a = 5;b = 2;b <= a	true
==	Equal to	a = 5;b = 2;a == b	false
!=	Not equal to	b = 2;b != 2	true

Notice:

, < , >= , <= can only support numeric type on both sides of the operators
== , != can support numeric type and reference type on both sides

Logical operators

It’s mainly use for logical operations.

Common logical operators in Java:

Logical operator	Definition	Example	Output
&&	Logical and	a && b	if a and b both are true,then return true
\|\|	Logical or	a \|\| b	if one of a and b is true,then return true
!	Logical not	!a	if a is false,then return true
^	Exclusive or	a ^ b	if a and b only have one of them is true,then return true

Conditional operator

Conditional operator is also called Ternary Operator

syntax: Boolean expression ? expression 1 :expression 2

If the value of boolean expression is true,then return the value of expression 1;If it’s false,then return the value of expression 2.

int result = (8 > 5) ? 1 : 0;
System.out.println(result);
//output
//1

The priority level of operators

Priority	Operators
1	()
2	var++ , var–
3	+(positive) , -(negative) , ++var , –var
4	(type)(type convert)
5	!(not)
6	* , / , %
7	+(plus) , -(minus)
8	< , <= , > , >=
9	== , !=
10	^
11	&&
12	\|\|
13	?:
14	= , += , -= , *= , /= , %=

Level 1 has the highest priority and level 11 has the lowest.

In real life,we usually use brackets to assist priority management.

Arithmetic operators

Assignment operators

Comparison operators

Logical operators

Conditional operator

The priority level of operators

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