keyboard entry

Get user input dynamically

//Guide Package
import java.util.Sccanner;

public static void main(String[] args){
	Scanner input = new Scanner(System.in);
	// Enter an integer data
	int num =  input.nextInt();

	//Enter a string data
	String name = input.next();

	//Enter a double data
	double money = input.nextDouble();
}

import java.util.Scanner;
public class IpuptDemo{
    public static void main(String[] args){
        Scanner input = new Scanner(System.in);
        System.out.println("Please enter an integer");
        int number = input.nextInt();
        System.out.println("What you entered is"+ number);
    }
}

operator

Assignment Operators

assignment
=

A very basic but very common operator. Its function is to assign the data on the right of the equal sign to the variables on the left

public static void main(String[] args){
   int m = 10;
   int k = 20;
}

Note: the assignment data must be consistent with the type (excluding automatic type promotion)

Arithmetic operator

addition	subtraction	multiplication	division	Modular operation
+	-	*	/	%

public static void main(String[] args){
   int m = 90;
   int k = 5;
   System.out.println( m+k );
   System.out.println( m-k );
   System.out.println( m*k );
   System.out.println( m/k );
   System.out.println( m%k );
}

Note: it is used for arithmetic and mathematical operations, following the mixed algorithm, and the function of% is to find the remainder. Multiplier use*

Compound Assignment

Add etc	Subtraction	Multiply, etc	Divide and so on	Module, etc
+=	-=	*=	/=	%=

public static void main(String[] args){
   int m = 10;
   int k = 20;
   int n = 105;
   System.out.println( m+=10 );
   System.out.println( m-=20 );
   System.out.println( k*=2 );
   System.out.println( m/=5 );
   System.out.println( m%=5 );
}

Self increasing and self decreasing operator

The operation symbols of + 1 or - 1 on their own basis are divided into pre + +, post + + and pre -, post -

class PlusDemo{
  
  public static void main(String[] args){
 
      int age = 30;
      age--;    
      --age;
      
      //Whether + + -- before or after, the influence on the variable itself is to determine + 1 or - 1
      System.out.println(age);// 30
      
      System.out.println("-------------------------------------");
      int money = 100;
      System.out.println(--money); // 99
      System.out.println(money--); // 99
      System.out.println(money); // 98
      // For + + -- expressions, the position of + + -- is influential, with immediate computability before and delay computability after.
    }
}

Note: the pre + + (pre –) is calculated by itself first, and then the value is given; Post + + (post –) give the value first, and then calculate by yourself

Relational operator

greater than	less than	Less than or equal to	Greater than or equal to	equal	Unequal
>	<	<=	>=	==	!=

public static void main(String[] args){
   int m = 10;
   int k = 20;
   System.out.println( m>k );
   System.out.println( m<k );
   System.out.println( m>=k );
   System.out.println( m<=k );
   System.out.println( m==k );
   System.out.println( m!=k );
}

Note: it is used to compare the size relationship of data, and the operation result is Boolean; Note the difference between relational operators and assignment operators

Logical operation

And (short circuit)	Or (short circuit)	wrong	And (without open circuit)	Or (no short circuit)
&&	||	!	&	|

public static void main(String[] args){
   int m = 10;
   int k = 20;
   System.out.println( m>0 && k>0 );
}

Note: it is used for multi condition logic judgment, and the operation result is Boolean; Pay attention to the short circuit

ternary operator

Three eyes
? :

public static void main(String[] args){
   int m = 10;
   int k = 20;
   int t = 1>0?m:k;
}

Note: it can be used for logical judgment and assign values to variables according to the judgment results

Bitwise Operators

Bitwise AND	Bitwise OR	Bitwise XOR	Bitwise inversion	Shift left	Shift right	unsigned right shift
&	|	^	~	<<	>>	>>>
Same as 1	If there is one, there is one	The difference is 1 and the same is 0	0, 1 interchange	Move left	Move right	Move to the right without retaining the negative sign

public static void main(String[] args){
   int m = 10;
   int k = 20;
   System.out.println( m&k ); 
}

Application of bit operation

1. Exchange of two numbers (whether it can be used or not)

public static void main(String[] args){
   int m = 10;
   int k = 20;
   
   m ^= k;
   k ^= m;
   m ^= k;
}

1. Check whether the two IP addresses are in the same network segment

Precedence and associativity of operators

1. What is the priority of operators?
   The order in which operators are processed when the operation is completed
2. What is associativity?
   Operator deals with the order of operands, which is divided into left associativity and right associativity
3. Multiple operators with the same priority may appear in an expression. At this time, the operator must be evaluated first through associativity judgment

Note: priority shall be considered before combination
Example: ab+a + +?
+The lowest priority, left associativity, first calculate ab, then a + +, and finally calculate+