Java Process Control Statements

first, sequential statements

Statement: A semicolon-delimited code is called as a statement

Note: No code is written just a semicolon, but also a statement, called an empty statement

Second, Judgment (If...else)

Note: If there is only one statement in the curly braces, the curly braces can be omitted

Format one:

if (judging condition) {

Code block 1 for execution;

Code block 2 for execution;

... ；

code block n executed;

}

Format two:

if (judging condition) {

Code block 1 for execution;

... ；

code block n executed;

}else{

Code block 1 for execution;

... ；

code block n executed;

}

Format three:

if (judging condition 1) {

Code block 1 for execution;

}else if (judging condition 2) {

Execute the statement;

}else if (judging condition 3) {

Execute the statement;

}

Example:

import java.util.scanner;//Import Package Import java.util.scanner, use Scanner This class, fixed usage scanner sc=new  Scanner (system.in), Int nextint = sc.nextint () Gets the number entered by the user  public class demo1 {     public static void main (String[] args)  {     scanner sc = new scanner (system.in);     system.out.println (" Please enter a number: ");     int nextint = sc.nextint ();    if  ( nextint %2 == 0)  {        system.out.println ( Nextint + ": is an even number");    } else {         system.out.println (nextint + ": is an odd number");    }     System.out.println ("over");      }}  //run result [[Email protected] java ]# javac demo1.java[[email Protected] java]# java demo1 Please enter a number: 33: It's an odd over. 

 

[[Email protected] java]# cat demo2.javaimport java.util.scanner;public class  demo2 {    public static void main (String[] args)  {         scanner sc = new scanner (System.in);         system.out.println ("Please enter a number:");         double score = sc.nextdouble ();         char  grade;        if  (score >=90)  {             grade =  ' A ';         }        else if  (score >=  80)  {            grade =  ' B ';         }        else if  (score >=  60)  {            grade =  ' C ';           }         else {            grade =  ' D ';         }         System.out.println (grade);     } } //run result [[email protected] java]#  java demo2 Please enter a number: 78.4C

 

Import java.util.scanner;public class demo3 {    public static  void main (String[] args)  {    Scanner sc = new  Scanner (system.in);     system.out.println ("Please enter Year:")     int year  = sc.nextint ();    boolean isleapyear =  (year %4 ==  0);    isleapyear = isleapyear &&  (year %100 ! = 0);     isleapyear = isleapyear | |   (year %400 ==0);    if  (isleapyear)  {         system.out.println (year + ": Is run Year");    } else {         system.out.println (year + ": Common Year");     }    } } //run Results [[email protected] JAVA]# JAVA DEMO3 Please enter the year: 20182018: Yes common year 

III. Choice of Judgment Statement (switch)

Format:

switch (expression) { Case takes value 1: Execute the statement; Break Case takes value 2: Execute the statement; Break ...... Default Execute the statement; Break }

Switch statement features:

1) The switch statement chooses only four types: Byte,short,int,char;

2) between case and default no order, first judge all case, no matching case execution default;

3) The switch statement stops with the following conditions: The break keyword is encountered or the curly brace of the end switch statement;

4) If the matching case or default does not have a corresponding break, then the program will continue to execute downward until a break is encountered or the end of the switch ends;

5) The value in the switch case must have the same data type as the value of the switch expression

Example:

[[Email protected] java]# cat demo4.javaimport java.util.scanner;public class  demo4 {    public static void main (String[] args)  {     scanner sc = new scanner (system.in);     double  x = sc.nextdouble ();     string z = sc.next ();     double y = sc.nextdouble ();    switch  (z)  {     case  "+":         system.out.println ("x+y=")  + (x+y));        break;    case  "-":         system.out.println ("x-y="  + (x-y));         break;    case  "*":         system.out.println ("x*y=" + (x*y));        break;    case "/":         system.out.println ("x/y="  + (x/y));         break;    default:         SYSTEM.OUT.PRINTLN ("not reliable");        break;     }       }} //Running Results [[email protected] java]# java  demo44+5x+y=9.0

Four, while loop

Description: The condition is judged first, the loop body is executed only if the condition satisfies.

Format:

while (conditional expression)

{

Execute the statement;

}

Example

[[Email protected] java]# cat demo5.javaimport java.util.scanner;public class  demo5 {public static void main (String[] args)  {int num =  ( int) (Math.random () *100) +1; Scanner sc = new scanner (system.in);int guessnum = -1; while  ( Guessnum != num)  {    system.out.println ("Please enter the number between 1-100:");     guessnum = sc.nextint ();    if  ( guessNum == num )  {       system.out.println ("in the!");      } else if  ( guessnum > num)  {        SYSTEM.OUT.PRINTLN ("Big value!");      } else {       system.out.println (" The value is small! ");      }} }} //run Results [[EMAIL PROTECTED]&Nbsp;java]# javac demo5.java[[email protected] java]# java  Demo5 Please enter the number between 1-100:12 value is small! Please enter a number between 1-100:

v. Do and loop

Note: The loop body is executed first, then the condition is satisfied, and then the loop body is resumed.

Features: The loop body is executed at least once, whether or not the condition is satisfied

Format

Do { Execute the statement; }while (conditional expression);

Example

[[Email protected] java]# cat demo6.javaimport java.util.scanner;public class  demo6 {public static void main (String[] args)  {int num =  ( int) (Math.random () *100) +1; Scanner sc = new scanner (system.in); int guessnum = -1;int count =  0; do {    system.out.println ("Please enter a number between 1-100:");     Guessnum = sc.nextint ();    if  ( guessnum == num)  {        SYSTEM.OUT.PRINTLN ("In!");      } else if  ( guessnum > num)  {        SYSTEM.OUT.PRINTLN ("Big value!");      } else {       system.out.println (" The value is small! ");      }    count++;}  while  (&NBsp;guessnum != num);  system.out.println ("The number to be guessed is:"  +num + "  you guessed it altogether:"  +count  + "Times");  }} //Run result [[email protected] java]# javac demo6.java[[email  PROTECTED] JAVA]# JAVA DEMO6 Please enter the number between 1-100:10 value is big! Please enter the number between 1-100:5 value is big! Please enter the number between 1-100:4 value is big! Please enter the number between 1-100:2! The number to guess is:2  you guessed it: 4 times.

Six, for Loop

Format:

for (initialize expression; loop condition expression; post-loop action expression) {

Execute the statement;

}

Example:

[[email protected] java]# cat demo7.javapublic class demo7 {     public static void main (String[] args)  throws interruptedexception  {    for  (int i=1;i<=9;i++)  {         for  (int j=1;j<=i;j++)  {             system.out.print (i + "*"  +j + "="  + (i*j)  + "\ T");             thread.sleep (;      )       }            System.out.println (" ");        }    }}   //run Results [[email protected] java]# javac demo7.java[[email protected] java]#  java demo71*1=1   2*1=2  2*2=4   3*1=3  3*2=6  3*3=9    4*1=4  4*2=8  4*3=12 4*4=16  5*1=5  5*2=10 5*3=15  5*4=20 5*5=25  6*1=6  6*2=12 6*3=18 6*4=24 6*5=30 6*6=36   7*1=7  7*2=14 7*3=21 7*4=28 7*5=35 7*6=42 7*7=49  8*1 =8  8*2=16 8*3=24 8*4=32 8*5=40 8*6=48 8*7=56 8*8=64  9*1=9   9*2=18 9*3=27 9*4=36 9*5=45 9*6=54 9*7=63 9*8=72 9*9=81

Seven, break, continue keyword

Break: Statement following the termination statement

Continue: Jump out of this loop and perform the Next loop

Note: If continue appears at the end of the loop (the last statement), you can omit the

Java Process Control Statements