如何在循环中打印出方法

Question

I apologize but I am new to programming and I'm having difficulty coding a program. The original program is as follows:

import java.io.*;
import java.io.IOException;
import java.io.InputStreamReader;

class buildABoat{

    String boatName;      // Boat name
    void buildABoat(){      
        String BoatName;            
    }

    void nameTheBoat() {        
        try {           
            BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
            System.out.println("\n\nWhat should we name this vessel? \n\n");
            this.boatName = br.readLine();
            System.out.println("\n\nThe " + boatName + " is ready to sail!\n");             
        }           
        catch (IOException e) {                 
        }   
    }
}

class proj1{

    public static void main(String[] arg){

        buildABoat boat1;
        buildABoat boat2;
        buildABoat boat3;
        buildABoat boat4;
        buildABoat boat5;

        boat1 = new buildABoat();
        boat2 = new buildABoat();
        boat3 = new buildABoat();
        boat4 = new buildABoat();
        boat5 = new buildABoat();

        boat1.nameTheBoat();
        boat2.nameTheBoat();
        boat3.nameTheBoat();
        boat4.nameTheBoat();
        boat5.nameTheBoat();

        System.out.println("(Press ENTER to exit)");

        try {           
            System.in.read();
        }           
        catch (IOException e) {         
            return;
        }
    }
}

This produces the following:

What should we name this vessel?
Enterprise
The Enterprise is ready to sail!
What should we name this vessel?
Columbia
The Columbia is ready to sail!
What should we name this vessel?
Challenger
The Challenger is ready to sail!
What should we name this vessel?
Atlantis
The Atlantis is ready to sail!
What should we name this vessel?
Endeavor
The Endeavor is ready to sail!
(Press ENTER to exit)

I tried to change this to the following:

import java.io.*;
import java.io.IOException;
import java.io.InputStreamReader;

class buildABoat{    
    String boatName;      // Boat name

    void buildABoat(){
        String BoatName;
    }

    void nameTheBoat() {
        try {           
            BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
            System.out.println("\n\nWhat should we name this vessel? \n\n");
            this.boatName = br.readLine();
            System.out.println("\n\nThe " + boatName + " is ready to sail!\n");             
        }           
        catch (IOException e) {                 
        }   
    }
}

class proj1{

    public static void main(String[] arg){

        Boat[] boat;            
        boat = new Boat[5];    
        for(int i = 0; i <= Boat.Length; i++){          
            nameTheBoat();          
        }           
        System.out.println("(Press ENTER to exit)");

        try {           
            System.in.read();
        }           
        catch (IOException e) {         
            return;
        }
    }
}

This of course produces the following error:

proj1.java:71: error: cannot find symbol
                for(int i = 0; i <= Boat.Length; i++){
                                        ^
  symbol:   variable Length
  location: class Boat
proj1.java:73: error: cannot find symbol
                        nameTheBoat();
                        ^
  symbol:   method nameTheBoat()
  location: class proj1
2 errors

What am I missing in the new program?

Answer 1

使用小写长度

for(int i = 0; i <= Boat.length; i++)

Answer 2

Try doing boat.nameTheBoat() instead of just nameTheBoat()

Also

for(int i = 0; i <= boat.length; i++){          
        boat[i].nameTheBoat();          
    }    

boat is the instance of the class Boat (probably should be buildABoat ). These look like they're compiler errors and not runtime errors, so the compiler should give you some hint (as it does) as to the exact line numbers.

Answer 3

You must try to calculate the length on the object rather than the class. So, it should be boat.length, where boat is your object here

You call a method using the class name, if the method is a static method.

Answer 4

As Nurlan mentions, the first error is because you're using a capital L for the length property of an array. The actual property begins with a lowercase l.

The second error is because the method nameTheBoat is part of the class named buildABoat , but you're trying to invoke it as if it were part of your main class. You need an instance of a buildABoat object in order to invoke this method.

One other suggestion: to comply with java naming conventions, you should NOT begin the name of a class with a lowercase letter. Classes should always start with a capital letter. Methods should always begin with a lowercase letter.

Answer 5

where you have

nameTheBoat();

in your for() loop you need to have

boat[i] = new Boat();
boat[i].nameTheBoat();

The reasons are: 1) nameTheBoat() is a method that only operates on objects of type Boat . You are not giving it any object to work on. 2) boat[] = new Boat[5]; initializes an Array object, but doesn't create the 5 new Boat s in the Array object. So you need to create each of those 5 Boat s before you can run a Boat method on them. Otherwise you'll get a null pointer error.

EDIT: and of course as others mentioned, boat.length is the length of the array boat , boat.Length is wrong.

Enjoy!

Answer 6

The object array you have created is boat = new Boat[5]; . Ideally you whole code should be like this

Boat[] boat = new Boat[5];    
for(int i = 0; i <= Boat.Length; i++){          
boat[i] = new Boat();
boat[i].nameTheBoat();          
}

Answer 7

You have a few problems.

One is that boat as an array

Boat[] boat;            
boat = new Boat[5];    
for(int i = 0; i <= Boat.Length; i++){          
    nameTheBoat();          
} 

To access the array length it would be boat.length instead of what you have.

The next problem I see is your call to nameTheBoat() . That method is part of the buildABoat class.

Answer 8

This code looks like a constructor with accident.

class buildABoat{    
    String boatName;      // Boat name

    void buildABoat(){
        String BoatName;
    }

If void buildABoat () would be a method (void says so), why would you declare a local variable in it, and not use it?

And don't repeat the name of a well named attribute as comment.

class BuildABoat {    
    private String boatName;   

    public BuildABoat (String name) {
        boatName = name;
    }

This would make some sense. You now have a class, which can be instantiated by passing a boatname, which is preserved in the class.

In your Proj1-Class, you split declaration and initialisation. This is a bad habit. Sometimes it's not avoidable, but if it is, avoid it.

class Proj1 {

    public static void main(String[] arg){

        BuildABoat [] boat = new BuildABoat[5];    
        for(int i = 0; i <= boat.length; i++) {
            // to make this work, we have to change the 
            // buildABoat
            boat[i] = new BuildABoat (BuildABoat.nameTheBoat ());
        }
        System.out.println ("(Press ENTER to exit)");
        try {           
            System.in.read ();
        }           
        catch (IOException ignored) {         
            return;
        }
    }
}

The method nameTheBoat has to be static, if we call it without actually having a (builda)boat already.

public static String nameTheBoat () {
    try {           
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        System.out.println ("\n\nWhat should we name this vessel? \n\n");
        String s = br.readLine ();
        System.out.println ("\n\nThe " + s + " is ready to sail!\n");
        return s;
    }
      catch (IOException e) {
        return "";
    }   
}

I hope the code does a little what you intended.