为什么输出显示“null”？

Question

import java.lang.*;

public class TriangleType {
    int side1, side2, side3;  
    String kind;

    public TriangleType(int a, int b, int c) {
        side1 = a;
        side2 = b;
        side3 = c;

        if (a==b || b==c)
            kind = "Equilateral";
    }

    public static void main (String[]args)  {
        TriangleType triangle1 = new TriangleType(12, 13, 14);

        System.out.println("The sides are " + triangle1.side1 + " " +triangle1.side2 + " " +triangle1.side3);
        System.out.println("Triangle type: " + triangle1.kind );

        System.exit(0);
    }
}

The output is:

The sides are 12 13 14
Triangle type: null

How can I make the triangle type output to show "equilateral"?

Answer 1

First of all, your equilateral formula is wrong:

if (a==b || b==c)
kind = "Equilateral";

Should be

if (a==b && b==c)
kind = "Equilateral";

Second, the triangle you are creating needs equal sides to be equilateral

   TriangleType triangle1 = new TriangleType(12, 12, 12);

Also, IMO if the triangle is not equilateral, you should set it kind to something else ("not equilateral"?)

You also might want to think of getting rid of the kind member variable, as your equilateral function can be calculated when needed

Answer 2

The reason is that this triangle (12 13 14) is not equilateral. If you make it equilateral, say (a = b = c = 12), then the output of the triangle type will be "equilateral"

    public class TriangleType {


int side1, side2, side3;
String kind;


public TriangleType(int a, int b, int c) {

    side1 = a;
    side2 = b;
    side3 = c;

    if (a==b || b==c)
        kind = "Equilateral";

}


public static void main (String[]args)  {



    TriangleType triangle1 = new TriangleType(12, 12, 12);

    System.out.println("The sides are " + triangle1.side1 + " " +triangle1.side2 + " " +triangle1.side3);
    System.out.println("Triangle type: " + triangle1.kind );

    System.exit(0);

}

}

Answer 3

Because no one of this condition in if-statement is not true. You are set a sides of triangle, but each of this side is not equal. Seems like you should set default value for kind