Select Statement
Analyzing select statement statements also known, there are two kinds of writing, one is the if statement, one is the switch statement. Here we describe in detail the use of these two statements.
If the judge sentences
- The first form of the if statement: if
format:
Implementation process
- First, determine the relationship between the expression to see the result is true or false
- If the statement is true on the implementation of the body
- If false statement is not executed body
Execution flow as shown in FIG.
Code Example
package MyCode; public class Demo01If { public static void main (String [] args) { // 3 variables int A =. 1 ; int B = 2 ; int C =. 1 ; // relational expression determining true or to false IF (A == b) { System.out.println("a == b"); } IF (A == C) { // braces the body of code, the implementation of relational expression is true System.out.println ( "A == C" ); } System.out.println ( "Other statements" ); } }
The result of code execution
- The second form of the if statement: if ... else
format:
Implementation process
- First, determine the relationship between the expression to see the result is true or false
- If the statement is true on the implementation of 1
- If false statement on the implementation of 2
Code execution flow as shown below
Code Example
package MyCode; public class DemoIfElse { public static void main (String [] args) { // determines the given data is odd or even // define the variable int I = 22 is ; // Analyzing relational expression to see the result is true or to false IF ( 0% 2 == I ) { // to true if executed back braces code System.out.println ( "remainder is 0, an even number" ); } Else { // to false on the implementation of the code behind braces else System.out.println ( "the remainder is not 0, an odd number" ); } } }
The result of code execution
- The third form of the if statement: if ... else if ... else
format:
Implementation process
- First, determine the relationship between the expression 1 to see the result is true or false
- If the statement is true on the implementation of the body 1, the relationship between expression and body behind the statement is not executed.
- If it is false to continue to determine the relationship between the expression 2 to see the result is true or false
- If the statement is true on the implementation of the body 2, the relationship between expression and body behind the statement is not executed.
- If it is false to continue to determine the relationship between the expression ... see the result is true or false
- …
- If there is no relationship between the expression is true, then the statement is executed body n + 1.
Code execution flow as shown below
Code Example
package MyCode; public class DemoIfElseExt { /* Specifies the test scores to determine student grades 90-100 Excellent 80-89 Good 70-79 good 60-69 pass 60 The following fail */ public static void main(String[] args) { int score = 100; if (score < 0 || score > 100) { System.out.println ( "Your achievement is wrong" ); } else if (score >= 90 && score <= 100) { System.out.println ( "Your achievements belong excellent" ); } else if (score >= 80 && score < 90) { System.out.println ( "Your achievements belong to good" ); } else if (score >= 70 && score < 80) { System.out.println ( "Your achievements belong to good" ); } else if (score >= 60 && score < 70) { System.out.println ( "Your achievements belong to fail" ); } else { System.out.println ( "Your achievements belong to fail" ); } } }
The result of code execution
if statement and the ternary operator exchange
In some simple applications, if the statement is a ternary operator can be used interchangeably. For example: selecting the maximum value of several figures
Select statement switch
format:
Implementation process
- First, calculate the value of the expression
- Secondly, compare and order case, if there is a corresponding value, will execute the corresponding statement in the process of implementation, it encounters a break will end.
- Finally, if the case were all expressions and values do not match, it will execute the default statement body part, then the program ends off
Code execution flow as shown below
Code Example
public class Demo07Switch { public static void main (String [] args) { // definition of variables, of the week is determined int NUM =. 4 ; // Switch statement to achieve select Switch (NUM) { Case . 1 : System.out.println ( "Monday" ); BREAK ; Case 2 : System.out.println ( "Tuesday" ); BREAK ; Case 3 : System.out.println ( "Wednesday" ); BREAK ; Case 4 : System.out.println ( "Thursday" ); BREAK ; Case . 5 : System.out.println ( "Friday" ); BREAK ; Case 6 : System.out.println ( "Saturday" ); BREAK ; Case 7 : System.out.println ( "Sunday" ); BREAK ; default : System.out.println ( "Data unreasonable" ); break ; // the last break statement can be omitted, but it is strongly recommended not to omit } } }
The result of code execution
Note the use of the switch statement:
- The latter case a plurality of values can not be repeated.
- Switch parentheses behind which only the following data types: basic data types: byte / short / char / int reference Data Type: String String, enum enum
- The switch statement format can be very flexible: before and after the order can be reversed, and break statement can also be omitted.
- In a switch statement, if the latter case is not writing break, will appear penetration phenomenon, which is not a value judgment in the case, run directly back, until it encounters a break, or the end of the whole switch