Select knowledge points of structure

if Single choice structure

import java.util.Scanner;
public class IfDemo01 {

public static void main(String[] args) {
	Scanner sc=new Scanner(System.in);
	System.out.println(" Please enter the content ");
String str=		sc.nextLine();
//equals Determines whether the strings are equal 
if(str.equals("hello")){
System.out.println(str);
}
System.out.println("END");
	sc.close();
}
}
 Please enter the content 
hello
hello
END

if Double choice structure

1. grammar ：

if( Boolean expression 1){
// If the expression 1 The value of is true Execute code 
}elseif( Boolean expression 2){
// If the expression 2 The value of is true Execute code 
  }elseif( Boolean expression 3){
 // If the expression 3 The value of is true Execute code 
  }else{
  // If none of the above Boolean expressions are true Execute code 
  }

2. Case study

import java.util.Scanner;
public class IfDemo02 {
	public static void main(String[] args) {
		Scanner sc=new Scanner(System.in);
		int score=sc.nextInt();
		if(score==100){
			System.out.println(" Congratulations, full mark ");
		}else if(score<100&&score>=90){
			System.out.println("A level ");
		}else if(score<90&&score>=80){
			System.out.println("B level ");
		}else if(score<80&&score>=70){
			System.out.println("C level ");
		}else if(score<70&&score>=60){
			System.out.println("D level ");
		}else if(score<60&&score>=0){
			System.out.println(" fail, ");
		}else{
			System.out.println(" The results are illegal ");
		}

	}

3.if A statement can have at most one else sentence ,else Statements in else if After statement ,

if A statement can have several else if sentence , They have to be in else The statement before , Once one of them else if The statement is detected as true, Other else if as well as else Statement will skip execution .

• Nested if structure ：

• 1. grammar ：

  if( Boolean expression 1){
  // If the Boolean expression 1 The value of is true Execute code 
  if( Boolean expression 2){
  // If the Boolean expression 2 The value of is true Execute code 
  }
  }

• switch Multiple choice structure

• There is another way to implement the multi-choice structure switch case sentence .

• switch case Statement to determine whether a variable is equal to a value in a series of values , Each value is called a branch

• switch The variable type of the statement can be ：

  1.byte,short,int perhaps char.

  2. from javase7 Start switch Support string Sting type .

  3. meanwhile case Label must be a string constant or literal .

• grammar ：

• switch(exoression){
  case value:
  // sentence 
  break;// Optional 
  case value:
  // sentence 
  break;// Optional 
  // You can have any number of case sentence 
  default：// Optional 
  // sentence 
  }

• Case study ：

  public class SwitchDemo01 {
  
  	public static void main(String[] args) {
  		//case through 
  		char grade='F';
  		switch(grade){
  		case 'A':
  			System.out.println(" good ");
  			break;
  		case 'B':
  			System.out.println(" good ");
  			break;
  		case 'C':
  			System.out.println(" pass ");
  			break;
  		case 'D':
  			System.out.println(" Make persistent efforts ");
  			break;
  		case 'E':
  			System.out.println(" Fail ");
  			break;
  			default:
  				System.out.println(" Unknown level ");
  		}
  
  	}
  
  }

  public class SwitchDemo02 {​    public static void main(String[] args) {        String name=" Juen-Kai Wang ";        switch(name){        case " Juen-Kai Wang ":            System.out.println(" Wang Junkai is so handsome ");            break;        case " hanah ":            System.out.println(" Wang Yuan is really handsome ");            break;        case " Jackson Yi ":            System.out.println(" Yiyang Qianxi is really handsome. ");            break;            default:                System.out.println("TFBOYS The root is MiaoHong , The development will be better and better ");        }​    }​}