# Java基本運算符

Java提供了一組運算符豐富的操縱變量。我們可以把所有的Java操作符為以下幾組：

• 算術運算符

• 關係運算符

• 位運算符

• 邏輯運算符

• 賦值運算符

• 其它運算符

## 算術運算符：

+ Addition - Adds values on either side of the operator A + B = 30
- Subtraction - Subtracts right hand operand from left hand operand A - B = -10
* Multiplication - Multiplies values on either side of the operator A * B = 200
/ Division - Divides left hand operand by right hand operand B / A = 2
% Modulus - Divides left hand operand by right hand operand and returns remainder B % A = 0
++ Increment - Increases the value of operand by 1 B++ =21
-- Decrement - Decreases the value of operand by 1 B-- =19

## 關係運算符：

== Checks if the values of two operands are equal or not, if yes then condition becomes true. (A == B) is not true.
!= Checks if the values of two operands are equal or not, if values are not equal then condition becomes true. (A != B) is true.
> Checks if the value of left operand is greater than the value of right operand, if yes then condition becomes true. (A > B) is not true.
< Checks if the value of left operand is less than the value of right operand, if yes then condition becomes true. (A < B) is true.
>= Checks if the value of left operand is greater than or equal to the value of right operand, if yes then condition becomes true. (A >= B) is not true.
<= Checks if the value of left operand is less than or equal to the value of right operand, if yes then condition becomes true. (A <= B) is true.

## 按位運算符：

Java定義了幾個位運算符，它可以應用到整數類型，長型，整型，短整型，字符和字節。

a = 0011 1100

b = 0000 1101

-----------------

a&b = 0000 1100

a|b = 0011 1101

a^b = 0011 0001

~a  = 1100 0011

& Binary AND Operator copies a bit to the result if it exists in both operands. (A & B) will give 12 which is 0000 1100
| Binary OR Operator copies a bit if it exists in either operand. (A | B) will give 61 which is 0011 1101
^ Binary XOR Operator copies the bit if it is set in one operand but not both. (A ^ B) will give 49 which is 0011 0001
~ Binary Ones Complement Operator is unary and has the effect of 'flipping' bits. (~A ) will give -61 which is 1100 0011 in 2's complement form due to a signed binary number.
<< Binary Left Shift Operator. The left operands value is moved left by the number of bits specified by the right operand. A << 2 will give 240 which is 1111 0000
>> Binary Right Shift Operator. The left operands value is moved right by the number of bits specified by the right operand. A >> 2 will give 15 which is 1111
>>> Shift right zero fill operator. The left operands value is moved right by the number of bits specified by the right operand and shifted values are filled up with zeros. A >>>2 will give 15 which is 0000 1111

## 邏輯運算符：

&& Called Logical AND operator. If both the operands are non-zero, then the condition becomes true. (A && B) is false.
|| Called Logical OR Operator. If any of the two operands are non-zero, then the condition becomes true. (A || B) is true.
! Called Logical NOT Operator. Use to reverses the logical state of its operand. If a condition is true then Logical NOT operator will make false. !(A && B) is true.

## 賦值運算符：

= Simple assignment operator, Assigns values from right side operands to left side operand C = A + B will assign value of A + B into C
+= Add AND assignment operator, It adds right operand to the left operand and assign the result to left operand C += A is equivalent to C = C + A
-= Subtract AND assignment operator, It subtracts right operand from the left operand and assign the result to left operand C -= A is equivalent to C = C - A
*= Multiply AND assignment operator, It multiplies right operand with the left operand and assign the result to left operand C *= A is equivalent to C = C * A
/= Divide AND assignment operator, It divides left operand with the right operand and assign the result to left operand C /= A is equivalent to C = C / A
%= Modulus AND assignment operator, It takes modulus using two operands and assign the result to left operand C %= A is equivalent to C = C % A
<<= Left shift AND assignment operator C <<= 2 is same as C = C << 2
>>= Right shift AND assignment operator C >>= 2 is same as C = C >> 2
&= Bitwise AND assignment operator C &= 2 is same as C = C & 2
^= bitwise exclusive OR and assignment operator C ^= 2 is same as C = C ^ 2
|= bitwise inclusive OR and assignment operator C |= 2 is same as C = C | 2

## 其它運算符

Java 語言支持一些其他的運算符。

## 條件運算符 ( ? : ):

`variable x = (expression) ? value if true : value if false`

```public class Test {

public static void main(String args[]){
int a , b;
a = 10;
b = (a == 1) ? 20: 30;
System.out.println( "Value of b is : " +  b );

b = (a == 10) ? 20: 30;
System.out.println( "Value of b is : " + b );
}
}```

```Value of b is : 30
Value of b is : 20```

## instanceof運算符：

`( Object reference variable ) instanceof  (class/interface type)`

```public class Test {

public static void main(String args[]){
String name = "James";
// following will return true since name is type of String
boolean result = name instanceof String;
System.out.println( result );
}
}```

`true`

```class Vehicle {}

public class Car extends Vehicle {
public static void main(String args[]){
Vehicle a = new Car();
boolean result =  a instanceof Car;
System.out.println( result );
}
}```

`true`

## 優先級的Java操作符：

Postfix  () [] . (dot operator) Left to right
Unary  ++ - - ! ~ Right to left
Multiplicative   * / %  Left to right
Additive   + -  Left to right
Shift   >> >>> <<   Left to right
Relational   > >= < <=   Left to right
Equality   == !=  Left to right
Bitwise AND  Left to right
Bitwise XOR  Left to right
Bitwise OR  Left to right
Logical AND  &&  Left to right
Logical OR  ||  Left to right
Conditional  ?:  Right to left
Assignment  = += -= *= /= %= >>= <<= &= ^= |=  Right to left
Comma  Left to right