Java If Else语句的缩写

Question

I've been working on this code, its really basic but I just started working with Java and I don't know whats going on with it.

import java.util.Scanner;


public class Proj {


public static void main(String[] args) {

    //Create Scanner
    Scanner scanner = new Scanner(System.in);

    //Input Abbreviation
    System.err.print("Input METAR Abbreviation: "); 
    scanner.nextLine( );

    //Abbreviations
    String abb = "";
    if (abb.equals("B"))  {
        System.out.println ("Began At Time ");
    }
    else if(abb.equals("+")) {
        System.out.println ("Heavy intensity");
    }
    else if(abb.equals("-")) {
        System.out.println ("Light intensity");
    }
    else if(abb.equals("DZ")) {
        System.out.println ("Drizzle");
    }
    else if(abb.equals("E")) {
        System.out.println ("Ended At Time");
    }
    else if(abb.equals("HZ")) {
        System.out.println ("Haze");
    }
    else if(abb.equals("RA")) {
        System.out.println ("Rain");
    }
    else if(abb.equals("SN")) {
        System.out.println ("Snow");
    }
    else(abb !=NULL) {
        System.out.println("Unknown Abbreviation");
    }
    //Close scanner
    scanner.close( );
    }
}

So what I'm trying to do is when someone enters one of the abbreviations it prints out what it means, and if the abbreviation doesn't exist it prints out Unknown Abbreviation. So my problem is that when I run the code it prints Input METAR Abbreviation and you can enter a string but after that nothing happens, can someone help me out. Thanks

Answer 1

You call scanner.nextLine() but never actually capture or use its result. Then, you assign String abb= "" . This means abb will always be "" . That doesn't match any of your if conditions.

If you do String abb = scanner.nextLine( ); , you'll get what you want: the scanner will read the next line, and assign that value to abb .

Incidentally, I doubt this code compiles; NULL isn't a keyword in Java (Java is case-sensitive), and the else needs an if after it. But you also don't need to check for null , because scanner.nextLine() never returns it (if there's no next line, it just throws NoSuchElementException ). So the last bit should just be a plain else { .

Answer 2

There are some problems:

• You should assign the scanner.nextLine() result to a variable. In this case, I think you must assign it to abb :

  String abb = scanner.nextLine();

• Also, you forgot the if in the last condition:

   else if (abb != null) { System.out.println("Unknown Abbreviation"); } 

• And don't forget that Java is case-sensitive, so it must be null , not NULL .

Answer 3

May I sugest you use a switch statement, switch is much easier in your case instead of nested if, you can use

switch(condition){
case something:
//do stuff
}

For example

    switch(abb){
case "hello":
System.out.println("hi there")
break;
case "else string":
//do something 
break;
}

Good luck! Happy to help

Answer 4

您正在从Scanner中读取该行，但没有将其存储在任何地方，请按以下步骤进行更改：

String abb = scanner.nextLine( );