Javase the third day

Third Day ???? A

1: operator ( master )???? A

(1) Arithmetic Operators ???? A

(2) Assignment Operators ???? A

(3) comparison Operators ???? -

(4) logical Operators ???? -

(5) Bitwise Operators ( learn )???? -

(6) Ternary operators ???? -

2: Keyboard Entry ( master )???? -

3: Process Control Statements ???? -

4:if Statement ( master )???? -

(1) three different formats ???? the

(2) Precautions ???? -

(3) Case: ???? -

(4) ternary operators and if the relationship of the second form of the statement ???? -

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Third Day

1. Operator (master)???? (1) Arithmetic operators

???????? a:+,-, *,/,%,++,--

???????? The use of b:+

???????????? A: Addition

???????????? B: plus sign

???????????? C: String connector

???????? The difference between c:/and%

???????????? When the data is in division operation,/get is quotient,% get is remainder

???????? The use of d:++ and--

???????????? A: Their role is self-increment or self-reduction

???????????? B: Use

???????????????? * * Used alone

???????????????????? Put in front and back of the action data.

???????????????????? The a++ or ++a effect is the same.

???????????????? * * Participate in operation using

???????????????????? Put in front of operand: increment or decrement first, then participate in operation

???????????????????????? int a = 10;

???????????????????????? int b = ++a;

???????????????????? At the back of the operand: take part in the operation first, then self-increment or decrement

???????????????????????? int a = 10;

???????????????????????? int b = a++;

???? (2) Assignment operator

???????? a:=,+=,-=,*=,/=,%=, etc.

???????? B:= is called the assignment operator and is the most basic assignment operator

???????????? int x = 10; Assign 10 to the variable x of type int.

???????? C: Features of the extended assignment operator

???????????? Implicit automatic casts.

?????????????

???????????? Interview questions:

???????????????? Short S = 1;

???????????????? s = s + 1; (This will be error-guaranteed and will lose precision)

?????????????????

???????????????? Short S = 1;

???????????????? s + = 1; (Implicit automatic type conversion, no problem)

???????????????? Can you tell me which of the above code is wrong?

???? (3) Comparison operators

???????? a:==,!=,>,>=,<,<=

???????? B: Regardless of whether the operator is simple or complex, the end result is a Boolean type.

???????? C: Don't write = =

???? (4) Logical operators

???????? a:&,|,^,!, &&,| |

???????? B: Logical operators are used to concatenate Boolean types

???????? C: Conclusion

???????????? &: False if False

???????????? |: True if True

???????????? ^: The same is false, and the difference is true.

???????????????? Couple relationship.

????????????!: False if not true, true if not false

?????????????

???????????? &&: The result is the same as the &, except that it has a short-circuit effect. The left side is false and the right side is not executed.

???????????? | |: Results and | are the same, but with short-circuit effect. The left is true and the right side is not executed.

???? (5) bitwise operator (LEARN)

???????? Special usage of a:^

???????????? One data for another data bit XOR or two times, the number is unchanged

???????? B: Face question

???????????? A: Please implement the exchange of two variables

???????????????? * * Use of third-party variables

???????????????? * * with bitwise XOR OR operator

???????????????????? Left A,b,a

???????????????????? Right A^b

???????????? B: Please calculate the result of 2 times 8 in the most efficient way.

???????????????? 2<<3

???? (6) Ternary operator

???????? A: Format

???????????? Compare Expressions 1: expression 2;

???????? B: Execution Process:

???????????? The value of the comparison expression is evaluated first to see if it is true or false.

???????????? If true, the expression 1 is the result.

???????????? If False, the expression 2 is the result.

???????? C: Case:

???????????? A: Compare two data for equality

???????????? B: Get the maximum value from two data

???????????? C: Get the maximum value from three data

????????????

2: Keyboard entry (Master)

???? (1) in the actual development, the data is changed, in order to improve the flexibility of the program, we add keyboard input data.

???? (2) How to achieve it? Now remember

???????? A: Guide Package

???????????? import java.util.Scanner;

???????????? Position: On top of class

???????? B: Create an Object

???????????? Scanner sc = new Scanner (System. inch );

???????? C: Get Data

???????????? inti = sc. Nextint ();

???? (3) Adding the case of ternary operator to keyboard input improvement.

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3: Process Control statement

???? (1) sequential structure from top to bottom, executed sequentially

???? (2) Select structure???? Execute different code according to different choices

???? (3) Loop structure to do some repetitive code

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4. If statement (master)???? (1) Three formats

???????? A: Format 1

???????????? if (comparison expression) {

???????????????? Statement body;

????????????}

?????????????

???????????? Execution process:

???????????????? Judge the value of the comparison expression to see if it is true or false

???????????????? If true, the statement body is executed

???????????????? If False, the statement body is not executed

?????????

???????? B: Format 2

???????????? if (comparison expression) {

???????????????? Statement body 1;

????????????} else {

???????????????? Statement body 2;

????????????}

?????????????

???????????? Execution process:

???????????????? Judge the value of the comparison expression to see if it is true or false

???????????????? If true, the statement body is executed 1

???????????????? If False, the statement body 2 is executed

?????????????????

???????? C: Format 3

???????????? if (comparison expression 1) {

???????????????? Statement body 1;

????????????} else if (comparison expression 2) {

???????????????? Statement body 2;

????????????}

???????????? ...

???????????? else {

???????????????? Statement body n+1;

????????????}

?????????????

???????????? Execution process:

???????????????? Determine the value of the comparison expression 1 to see if it is true or false

???????????????? If true, the statement body is executed 1

???????????????? If false, continue to judge the value of the comparison expression 2 to see if it is true or false

???????????????? If true, the statement body is executed 2

???????????????? If false, continue to judge the value of the comparison expression 3 to see if it is true or false

???????????????? ...

???????????????? If all is not satisfied, execute the statement body n+1

???? (2) Precautions

???????? A: Comparing expressions whether simple or complex, the result is a Boolean type

???????? B:if statements control the body of a statement if it is a statement, you can omit the curly braces, if it is more than one, cannot be omitted.

???????????? Suggestion: Never omit.

???????? C: Generally, there are left curly braces, there is no semicolon, there is a semicolon, there is no left curly brace.

???????? D:else If there is no if, the comparison expression is not present.

???????? E: Three If statements are actually a statement, as long as there is one execution, the other is no longer executed.

???? (3) Case:

???????? A: Compare whether two numbers are equal

???????? B: Get the maximum value in two numbers

???????? C: Gets the maximum value in three digits (nested if statement)

???????? D: According to the grade of the result output corresponding

???????? E: According to the month, the corresponding season of the output

???????? F: Calculates the value corresponding to Y according to X and outputs

???? (4) The relationship between ternary operator and the second form of if statement

???????? All ternary operators can be implemented, and the second form of the IF statement can be implemented.

???????? Conversely, it is not established.

?????????

???????? If the statement body that is controlled by the second format of the IF statement is an output statement, it is not possible.

???????? Because the ternary operator is an operator, you must have a result returned and cannot be an output statement.

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Javase the third day