如何打印ArrayList <Point>

Question

Generally ArrayList will print nicely with a primitive type. I need to print out an ArrayList cleanly, like it does with primitive types. Right now it gives me this:

[java.awt.Point[x=8,y=8], java.awt.Point[x=7,y=9], java.awt.Point[x=6,y=8] ...

I just need to print it without "java.awt.Point", the details I'm not so worried about. I'm not sure if I can do this with a loop, targeting the index of the arrayList or...

This is the code I have, it makes a "robot" move around a grid:

ArrayList<Point> moves = new ArrayList<Point>();

// code that moves it one square at a time 
// and then add the move to an array 

moves.add(new Point(this.getX(),this.getY()));  // makes a new point, adds it to the array

And then to print:

System.out.println("Robot 1 moves: "+r1.moves);

I'm totally open to different solutions if anyone has a better idea. Thanks in advance!

Answer 1

You can use an enhanced for loop ...

for (Point p : r1.moves) {
    System.out.println(p.x + "x" + p.y);
}

Take a look at The for Statement (it's towards the bottom) for more details

Answer 2

You'd probably want to either create your own Point object (edit: MadProgrammer fairly chastises me for not pointing out that you should have a bunch of other good reasons to extend or replace a built-in class in addition to just a custom toString() method), in which case you could override the toString() method, or create a helper method that'll create a well-formed string from your collection of Points.

For example:

public string MakeNicePointsString(ArrayList<Point> points)
{
    String pointsString = "";
    for (int i = 0; i < points.length(); i++)
    {
        pointsString += "x=" + points[i].x.toString() + "y=" + points[i].y.toString();
    }

    return pointsString;
}

Answer 3

Java 8 solution:

    moves.stream().forEach((p)-> System.out.print("[" + p.x +"," + p.y + "]"));

Full example:

    List<Point> lst = new ArrayList<Point>();
    lst.add(new java.awt.Point(1,2));
    lst.add(new java.awt.Point(1,8));
    lst.add(new java.awt.Point(7,2));
    lst.add(new java.awt.Point(6,6));
    System.out.print("[");
    lst.stream().forEach((p)-> System.out.print("[" + p.x +"," + p.y + "]"));
    System.out.print("]");

OUTPUT

[[1,2][1,8][7,2][6,6]]

Answer 4

重写Point类的toString方法，以使其打印x＆y坐标。

Answer 5

I know it is another kind of extending @MadProgrammer ;) because it is defining an annonymous inner class, but you can define an inline overriding for toString method like this :

Point p = new Point(10, 20){
     @Override
     public String toString(){
        return (getX() + ", "+ getY()) + "";
     }
};

System.out.println(p); // 10.0, 20.0

this works for this instance only