Arithmetic operator

Precautions for arithmetic operators

• 1. The sign of the result is the same as that of the module
• 2. In development, we often use% to judge whether it can be eliminated
• 3. "+" can be a connector. In addition to the string addition function, it can convert non string into string.

For example:

System.out.println("5+5="+5+5);//Convert non string to string

The results are:

5+5=55

• 4. Self increment / self decrement does not change the data type of its own variable

s1++;
++s1;//When used alone, the two formulas have no difference and will not change the data type of the variable itself

//There are differences when used with other operators. See the arithmetic operator table above

Assignment Operators

• 1. Symbol:=
  • When the data types on both sides of "=" are inconsistent, you can use automatic type conversion or forced type conversion principle for processing
  • Continuous assignment is supported

give an example:

int i1,j1;
i1 = j1 = 10;

• Extended assignment operators: + =, - =, * =, / =,%=
  • Extending the assignment operator does not change the type of the variable itself
    give an example:

int i1 = 10;
i1 +=  10; //Does not change the data type of the variable itself

Comparison operator

• 1. The results of comparison operators are boolean, that is, they are either true or false
• 2. The comparison operator '= =' cannot be mistakenly written as' = '
• 3. Explain
  • == ， != : You can use not only data of numeric type, but also data of reference data type, such as String type.
    give an example:

Account acct1 = new Account(1000);
Account acct2 = new Account(1000);
boolean b1 = (acct1 = acct2); //Compare whether two accounts are the same Account
boolean b2 = (acct1 != acct2);

• <, >, > =, < =: can only be used between numeric data types
• 4. instanceof subsequent supplement
  Typical code:

//Example 1
int i = 20;
int j = 19;
System.out.println(i == j);//false
System.out.println(i = j);//19

//Example 2
boolean b1 = false;
boolean b2 = true;
System.out.println(b1 == b2);
System.out.println(b1 = b2);

Logical operator

• 1. Logical operators are used to connect Boolean expressions. In Java, they cannot be written as 3 < x < 6, but should be written as x > 3 & x < 6. The result is also Boolean
  -2. The difference between "&" and "& &":
  • ① In single & case, the operation is performed on the right regardless of whether the left side is true or false
  • ② When double &, if the left is true, the right participates in the operation. If the left is false, the right does not participate in the operation

Typical code 1:

int x = 1;
int y = 1;
if(x++==2 & ++y==2)
	{
		x =7;
	}
System.out.println("x="+x+",y="+y);

int x1 = 1;
int y1 = 1;
if (x1++==2&&++y1==2)
	{
		x1 = 7;
	}
System.out.println("x1="+x1+",y1="+y1);

• 3. The difference between "|" and "|":
  • ||Indicates that when the left is true, the right does not participate in the operation

Typical code 2:

int x2 = 1;
int y2 = 1;
if(x2++==1|++y2==1)
   {
   	x2 = 7;
   }
System.out.println("x2="+x2+",y2="+y2);
   	
   
int x3 = 1;
int y3 = 1;
if(x3++==1||++y3==1)
   {
   	x3 = 7;
   }
System.out.println("x3="+x3+",y3="+y3);

• 4. The difference between XOR (^) and or (|) is that when both left and right are true, the result is false
  • Understanding: XOR pursues "difference"! The difference is true and the same is false

practice

class Test
{
	public static void main(String args[])
	{
		boolean x = true;
		boolean y = false;
		short z=42;
		if((z++==42)&&(y=true))
			z++;
		if((x=false) || (++z==45))
			z++;
		System.out.println("z="+z);
	}
}

result:

z = 46

Bitwise Operators

To be added

Ternary operator / ternary operator

• 1. Format: (conditional expression)? Expression: 1;
  • The conditional expression is true, and the result of the operation is expression 1; Is false, and the result of the operation is expression 2;
• 2. Expression 1 and expression 2 are of the same type. What I understand here is that both are basic data types. Basic data types and reference data types cannot be used at the same time

Correct example:

int m = 19;
int n =8;
int max = (m > n)? m : n;

Examples of errors:

String c1 = (m > n)? 2 :  "output";
String s1 = (m > n)? 'a' : "output"

• 3. Relation and difference between ternary operator and if else:
  • ① Ternary operators simplify if else statements
  • ② Ternary operators require that a result be returned
  • ③ The code block after if can have multiple statements
• 4. Ternary operators can be nested
• 5. Any ternary operator that can be used can be rewritten into an if else statement. On the contrary, it does not hold

For example, reasons for not holding water:

int m = 19;
int n =8;
if (m>n)
	{
		System.out.println(m);
	}
else
	{
		System.out.println("character string");
	}

// The following is an example of an error if the compilation fails
String ss1 = (m > n)? "character string" : m;
System.out.println(ss1);

• 6. If the program can use both ternary operators and if else statements, the ternary operator is preferred.
  • Reason: simplicity and high operation efficiency