Let’s first explain what operators are
Symbols that operate on variables or constants are called operators
Put together, it’s an expression
List of articles
- Arithmetic operator
- Incremental assignment operator
- Self increasing / Self – subtracting operator
- Relational operator
- Logical operators
- An operator
- Shift Operators （ Understanding can ）
- Ternary operator
- priority
- notes
Arithmetic operator
That is the most basic + – * / %
These are relatively simple to use , But should pay attention to / and % The use of
System.out.println(3/2); No 1.5, It is 1, because int/int What we should get is intSystem.out.println((float)3/2); 1.5System.out.println(3/(float)2); 1.5 As long as one is floating-point, the answer is floating-point System.out.println((float)(3/2)); 1.0 This is the first calculation 1 Re convert to 1.0
Be careful ： The divisor cannot be zero 0, By this mistake , Let’s take a brief look at Java A description of when something goes wrong , If you’re interested in anomalies , I’ll post a blog about anomalies later .
System.out.println(10%3); 110-3*3=1System.out.println(10%-3); 110-(-3)*(-3)=1System.out.println(-10%3); -1-10-(-3)*3=-1System.out.println(-10%-3); -1-10-(-3)*3=-1 It can be seen from the above formula that the sign of remainder is only related to the sign of the preceding number System.out.println(12.5/3); 0.5C We can't carry out decimal remainder in language , but java Sure
Incremental assignment operator
namely += -= *= /= %=
int a=2;a+=1 Equate to a=a+1 however java The incremental assignment operator in can automatically force type conversion example short b=1; b=b+2;// It's a warning ,b+2 After that, it will improve , Type mismatch b+=a;// In this way, the forced conversion is automatically completed += -= *= /= %= It's called the composition operator , All of them can help us make a cast
Self increasing / Self – subtracting operator
namely ++ 、- –
In front of ++ First ++ After use After ++ after ++ First use -- Empathy int a=1;int b=a++;b=1,a=2int a=1;int b=++a;b=2,a=2a++; or ++a; This is the moment a+1, There is no difference between
Relational operator
There are six relational operators ：== 、 >= 、 <= 、 > 、 < 、 !=
int a=1,b=2;System.out.println(a>b); falseSystem.out.println(a<b); trueSystem.out.println(a>=b); falseSystem.out.println(a<=b); trueSystem.out.println(a!=b); trueSystem.out.println(a==b); false
These expressions in brackets are Boolean expressions , The result is either true, Or false
Logical operators
&& It’s called logic and （ Or short circuit with ）,|| It’s called logic or ( Or short circuit or ),！ It’s called logical non
Boolean expression 1 && Boolean expression 2 As long as there's an expression for false, The whole expression is false If the expression 1 For false , The expression is no longer executed 2 example System.out.println(1>2 && 1/0); That was already said 0 Divisor will report an error , Will it report an error now ？ Can't , because 1>2 For false , Then it won't happen again 1/0 This expression has been changed , All that's printed on the screen is false
Boolean expression 1 || Boolean expression 2 (C Expressions in languages can be of other types ) As long as there's an expression for true, The whole expression is true If the expression 1 It's true , The expression is no longer executed 2 example System.out.println(1<2 && 1/0); What about the result ？ Same as above, because 1<2 It's true , Then it won't happen again 1/0 This expression has been changed , All that's printed on the screen is true
! Still combined with Boolean expressions !true == false!false == true
C Expressions in languages can be of other types ,Java It doesn’t matter 0 For false , Non zero is true
Not recommended &（ And ） and |（ or ）, Because they have to be executed on both sides , Short circuit evaluation is not supported
System.out.println(1>2 & 1/0);System.out.println(1<2 | 1/0); Both of these will be abnormal
An operator
There are four bit operators ：& | ^ ~
Bit operation means binary bit operation , All computers use binary to represent data （01 Sequence of composition ）, Bitwise operation is in accordance with each bit of the binary bit in order to calculate
Bitwise AND &： 0000 1011 0000 0101 result 0000 0001 The corresponding bits are 1 It's just 1, The rest are 0
Press bit or |： 0000 1011 0000 0101 result 0000 1111 The corresponding bits are 0 It's just 0, The rest are 1
Bitwise XOR ^： 0000 1011 0000 0101 result 0000 1110 The corresponding bit is different 1, Same as 0
According to the not ~： 0000 1011 result 1111 01000 become 1,1 become 0
Shift Operators （ Understanding can ）
There are three shift operators ：<< 、>> 、>>>( Use… For complement )
Shift left operator << It's like multiplication , move n position , The original number is multiplied by 2 Of n Power ( The right to repair 0)0000 0110 <<1 6 0000 0110 <<2 60000 1100 12 0001 1000 24
Shift right operator >> It's equivalent to division , move n position , Divide the original number by 2 Of n Power ( Fill in the sign on the left )0000 0110 >>1 6 0000 0110 >>2 60000 0011 3 0000 0001 1
Be careful ： Shift right operator pairs -1 of no avail (-1 The complement of is 32 individual 1, Moving right makes up for 1, Or -1)
unsigned right shift >>> Negative or not , Fill all the left 0-1>>>1 Move right and fill left 0, Become a very large positive number （ Binary for 0 Back 31 individual 1）
Be careful ： There is no unsigned shift left operator
Because the efficiency of computer calculation is higher than that of multiplication and division , When a code just multiplies and divides 2 Of n We can use shift operation instead of .
Ternary operator
Boolean expression ? expression 1： expression 2
Perform logical ： If the Boolean expression is true , Then execute the expression 1; If the Boolean expression is false , Then execute the expression 2
int a=1;int b=2;int max=a>b?a:b; You can nest int c=3;max=c>(a>b?a:b)?c:a>b?a:b;
priority
There is priority between operators , No need to remember , Just put parentheses where there may be ambiguity 
notes
- Documentation Comments
Generally used in front of methods and classes
I want to set up each of these class A document comment that automatically appears at the beginning Click this to teach you how to set up - Block annotation
Multiline comment /* hello world */
- Line notes
// int a=0;
Be careful ： The content of the notes should be accurate （ The code is consistent with the comments , Update notes in time ）, Medium length （ It can’t be too short , It’s not easy for others to understand ; It can’t be too long , It is not convenient for later maintenance ）.