Knowledge points of circular structure

1.while loop

• while It's a basic cycle , Its cycle structure is ：

  while( Boolean expression ){
  // Cycle content 
  }

• As long as the Boolean expression is true, The loop goes on and on

• A small number of cases require a loop to be executed all the time , For example, the server's request response monitoring and so on .

• The cycle condition is always true It's going to create a dead cycle , Our normal business should avoid dead circulation , It will affect the performance of the program or cause the program to jam and crash ！.

• Most of the time we stop the cycle , We need a way to invalidate the expression to end the loop .

• Case study ：

  public class WhileDemo01 {​    public static void main(String[] args) {        // Calculation 1+2+3+....+100        int i=0;        int sum=0;        while(i<=100){            sum=sum+i;            i++;        }        System.out.println(sum);​    }​}5050

  2.do......while loop

• do..while And whie be similar , The difference is do..while At least once .

• while Judge before you execute ,do...while Execute before judge .

• Case study ;

  public class DoWhileDemo01 {
  	public static void main(String[] args) {
  	int a=0;
  	while(a<0){
  		a++;
  		System.out.println(a);
  	}
  	System.out.println("************");
  	do{
  	a++;	
  	System.out.println(a);
  	}while(a<0);
  	
  	}
  
  }
  ************
  1

  3.for loop

• Make the cycle simpler .

• It is a general structure that supports iteration , It is the most effective and flexible structure

• grammar ：

  for( initialization ; Boolean expression ; to update ){
  // Code statements 
  }

  // Calculation 0-100 The sum of odd and even numbers 
  public class ForDemo02 {
  
  	public static void main(String[] args) {
  		int oddsum=0;
  		int evensum=0;
  		for(int i=0;i<=100;i++){
  			if(i%2==0){// even numbers 
  				evensum+=i;
  			}else{
  				oddsum+=i;
  			}
  		}
  		System.out.println(" The sum of odd numbers is "+oddsum);
  		System.out.println(" The sum of even numbers is "+evensum);
  	}
  
  }
   The sum of odd numbers is 2500
   The sum of even numbers is 2550

  4. stay java5 An enhancement mainly used for arrays is introduced in for loop

• grammar ：

  for( Statement statement : expression ){
  // Code sentence 
  }

•   expression ： Is the name of the array to access , Or the return value is an array .

• Statement statement ： Declare new local variables , The type of the variable must match the type of the array element , Its scope is limited to circular chunks , Its value is equal to the value of the array at this time .

• Case study ;

  public class ForDemo05 {public static void main(String[] args) {    int [] numbers={10,20,30,40,50};// Define an array     for(int x:numbers){        System.out.println(x);    }​}}1020304050