How to print list of string inside bracket? [closed]

问题

I am new to Java. I am facing a problem to print a list of string separated by commas inside brackets.

public class House extends Property { 
protected static List<String> paints;
public String paint;

public House() {
    super("House", 45);
    String paints = new String();
    System.out.print(paints);
}

public void addPaint(String paint) {
    this.paint = paint;
    ArrayList<String> House = new ArrayList<String>();
    House.add(" ");

public void display() {
    super.display();
    List<String> words = Arrays.asList(paint);
    StringJoiner strJoin = new StringJoiner(", ", " { ", " }");
    words.forEach((s)->strJoin.add(s));
    if (paint == null || "".equals(paint)) {
        System.out.print(" { }");
    }

    else {
    System.out.print(strJoin);
    }

public static void main(String[] args) {
        House house1 = new House();
        house1.addPaint("Red");
        house1.addPaint("Blue");
        house1.addPaint("Yellow");
        house1.display();
    }

It should be printed like this for a house with colors:

45 House { Red, Blue, Yellow }

Or like this for a house without color (empty):

45 House { }

However, the output of my code only prints the last added color:

45 House { Yellow }

Please help me. Thank you

回答1:

public class House {
    List<String> colors = new ArrayList<String>(); 
    public void addPaint(String color)
    {
        colors.add(color);        
    }
    public void display()
    {   String value = "";
        for (String color : colors)
        value += color + ", ";
        value = value.substring(0, value.length()-2);
        System.out.println("{ " + value + " }");
    }
}

public static void main(String[] args) {
    House house1 = new House();
    house1.addPaint("Red");
    house1.addPaint("Blue");
    house1.addPaint("Yellow");
    house1.display();
}

// Output: { Red, Blue, Yellow }

回答2:

You have declared paint as a String (and not a List of Strings) here.

public String paint;

And then you convert the String variable to a List.

List<String> words = Arrays.asList(paint);

Which is why the list words has only the single String which was added last with house1.addPaint(), which just assigns the String this.paint = paint; inside it.

There are many ways you can fix it. But I'll tell the one that requires the least amount of changes.

My suggestion:

public void addPaint(String paint) {
    paints.add(paint);
}

and

List<String> words = Arrays.asList(paints);

回答3:

To group a list of strings using a prefix and suffix you can use Collectors.joining(CharSequence delimiter, CharSequence prefix,CharSequence suffix)), example :

import java.util.List;
import java.util.stream.Collectors;

public class Test {
    public static void main(String[] args) {
        List<String> colors = List.of("Red", "Blue", "Yellow");
        String result = colors.stream().collect(Collectors.joining(" , ", "{", "}"));
        System.out.println(result);
    }
}

this will print {Red , Blue , Yellow} and if list is empty it will print {}

Note that:

I think you should review your model design ^^ !
I've used List.of() in my example to demonstrate the "how to", knowing that it requires java 9 or above

来源：https://stackoverflow.com/questions/64305106/how-to-print-list-of-string-inside-bracket

标签

java

string

printing

java.util.scanner

brackets