Java Learning Lesson 03

Java three major Process control

* Sequential control: The code executes sequentially from top to bottom;

* Condition control;

* Cycle control.

Conditional control: The condition has a true or false characteristic, and can only be true or false.

* If statement

Import java.util.scanner;public class scoredemo {public static void main ( String[] args) {System.out.println ("Please enter your score:"); Scanner sc=new scanner (system.in); Int score=sc.nextint ();          //  comparison expressions whether simple or complex, the result must be a Boolean type  if (score>=90)       &NBSP;&NBSP;&NBSP;&NBSP;SYSTEM.OUT.PRINTLN ("Excellent! ");          //if statement control Statement Body if it is a statement, the curly braces can be omitted;     if (score>=80&&score<90) {         system.out.println ("Good! ");       }     if (score>=60&&score<80) { &NBSP;&NBSP;&NBSP;&NBSP;&NBSP;&NBSP;&NBSP;&NBSP;&NBSP;SYSTEM.OUT.PRINTLN ("Pass! ");       }     if (score>=0&&score<60) {          system.out. println ("Less than a lattice!" ");       }}}

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* If......else If......else if (can be connected to n else if) ... else statement

The last else can be omitted, but it is recommended to retain else to ensure the integrity of the program and improve readability.

  import java.util.scanner;//Guide package, as long as the class is not Java.long package to guide the package;  public class  Agedemo{  public static void main (String[] args) {         //Keyboard Entry       system.out.println ("Please enter your Age:");       scanner sc=new scanner (system.in);       int age =sc.nextint ();       //enter the age into the loop to match the condition       if >60) {            system.out.println ("Old man!!! ");          }             else if (age>=40&&age<60) {             system.out.println ("Middle-aged!! ");           }  &Nbsp;    else if (age>=18&&age<40) {       &NBSP;&NBSP;&NBSP;&NBSP;&NBSP;&NBSP;SYSTEM.OUT.PRINTLN ("Boy!! ");           }       else {             system.out.println ("Underage!! ");           }       }}

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* Switch (judging value) {

Case value: Code of Implementation;

Break ;

Case value: Code of Implementation;

Break

Case value: Code of Implementation;

Break

Default: the Code of Implementation;

Break

}

the () after switch () can not be omitted;

A shape or character type followed by a switch;

Case value after plus: can only be literal constants (either, ' a ') or constant expressions (2*3)

Break out of a matching condition; break if the ellipsis program continues until it encounters a break, it jumps out of the loop.

Default: What is executed when no conditions are matched

public class switchdemo{    public  Static void main (String[] args) {    int food=5;     switch (food) {    case 1:    case 2:     case 3:system.out.println ("Eat dumplings today!!");     break;    case 4:system.out.println ("Eat rice today!");     BREAK;    CASE 5:SYSTEM.OUT.PRINTLN ("No food today!!!");     break;    case 6:system.out.println ("There's a treat today!");     break;    case 7:system.out.println ("Eat noodles today!!");     break;        }  }} 

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* Type of expression:

int a = 5;

A*3 (Result 15)

The output type of the expression evaluates to the type of the result of the expression

Double num = 1.5;

NUM * 4 (6.0, the type that the expression is ultimately treated as is the double type)

Loop control

* While loop

Structure:

while (loop condition) {

Loop-Implemented code

}

* Ask 1-50 (both sides are closed intervals), all even-numbered and.

Public class evennumdemo{    public static void main (String[]  args) {        int arr[]=new int[50];         int sum=0;        int i=0;           while (i<arr.length) {            arr[i]= (i+1);            if ((arr[i]%2)!=0) {                  sum+=arr[i];           }            i++;            }        system.out.println (the sum of even numbers of "1-50" is: "+sum) ;}}

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* do. While loop

Structure:

do{

Code of Implementation

}while (cyclic conditions);

* For Loop

The highest utilization rate;

Structure:

for (loop variable initialization; cyclic condition judgment; change of cyclic variable) {

The logic that loops need to implement

}

* Ask 1-100 natural number, where all the even and, all odd and, and seek all even and with all odd and difference.

Public class numsumdemo{    public static void main (String[]  args) {        int max_num=100;         int evenSum=0;        int oddSum=0;         int poor=0;         int j=0;        for (int i=0;i<max_num;i++) {             j=i+1;             if ((j%2)!=0) {                  oddsum+= (i+1);  //2 Not equal to 0: odd and             }else{                  evensum+= (i+1);  //even and            }          }         poor= ( Evensum-oddsum);          system.out.println ("1-100 even numbers:" +evenSum) ;          system.out.println ("1-100 Odd and for:" +oddsum);          system.out.println ("1-100 even and with odd and difference:" +poor);}}

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* Foreach Loop (not a regular Java-provided way of looping, he's just a Java-provided syntax for sugar)

foreach: A way to name a loop, a simplification of the general loop.

* Syntax sugar: For basic syntax, a simplified implementation is provided.

* Two keywords: applied to the loop control, the meaning of continue is to jump out of the cycle, break is the meaning of jumping out of the entire loop.

Nesting of loops:

public class stardemo{    public  Static void main (String[] args) {        int max_ Num=4;        for (int i=max_num;i>=0;i--) {             for (int j=0;j<i;j++) {                 system.out.print ("*");  //output, no line break             }             system.out.println ("*");  //output, default line wrapping          }}} 

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Java Learning Lesson 03