Java 3种方法从控制台获取输入详解

水深无声 2023-09-23 22:44 12阅读 0赞

3 ways by using

1.  Using BufferedReader class
2.  Using Scanner class
3.  Using Console class

# 1. Using BufferedReader class #

> > we can take input from the console by wrapping System.in into an InputStreamReader and passing it into the BufferedReader.  
> > It provides an efficient reading as the input gets buffered.

public class A{
        
    
        public static void main(String[] args) throws IOException {
        
            System.out.println("what's your name?");
            BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
            String name = reader.readLine();
            System.out.println(name);
        }
    }

what's your name?
    Amy (input context)
    Amy

# 2. Using Scanner class #

> > The Java `Scanner class` breaks the input into tokens using a **delimiter** that is **whitespace by default**.  
> > It provides many methods to read and parse various primitive values. Java Scanner class is widely used to parse text for string and primitive types using **a regular expression**. Java Scanner class extends **Object class and implements Iterator and Closeable interfaces**.

public class A{
        
    
        public static void main(String[] args){
        
            String str = "what's your name?/My name is Amy";
            //Create scanner with the specified String Object    
            Scanner scanner = new Scanner(str);
            System.out.println("Boolean Result: "+scanner.hasNextBoolean());
            scanner.useDelimiter("/");
            //Printing the tokenized Strings
            System.out.println("---Tokenizes String---");
    
            while(scanner.hasNext()){
        
                System.out.println(scanner.next());
            }
            //Display the new delimiter
            System.out.println("Delimiter used: " +scanner.delimiter());
            scanner.close();
        }
    }

Boolean Result: false
    ---Tokenizes String---
    what's your name?
    My name is Amy
    Delimiter used: /

# 3. Using Console class #

> >  *  The Java `Console class` is used to get input from the console.
> >  *  It provides methods to read texts and passwords.
> >  *  If you read the password using the Console class, it will not be displayed to the user.
> >  *  The java.io.Console class is attached to the system console internally.
> >  *  The Console class is introduced since 1.5. Consider the following example.

public class A{
        
        public static void main(String[] args){
        
            Console c = System.console();
            System.out.println("Enter your name: ");
            String n = c.readLine();
            System.out.println("Welcome "+n);
        }
    }

Enter your name: 
    Exception in thread "main" java.lang.NullPointerException
    	at model.A.main(A.java:15)