从double到int的可能有损转换？

Question

This is the message I get when I try to compile my code. What exactly does it mean and how can I fix this?

practice.java:13: error: incompatible types: possible lossy conversion from double to int
            pattern(t, length);
                       ^
Note: Some messages have been simplified; recompile with -Xdiags:verbose to get full output
1 error

Here is my code:

public static void main(String[] args){
    Turtle t = new Turtle();
    t.delay(30);
    pattern2(t, 50.0, 3);

}

public static void pattern2(Turtle t, double length, int level){
    double random = Math.random();
    if (level == 0){
        pattern(t, length);
    } else{
        t.color(150/level, 150/level, 150/level);
        pattern2(t, length, level -1);
        t.penup();
        t.backward(length*4.5);
        t.left(60);
        t.forward(length);
        t.right(60);
        t.backward(length/random);
        t.pendown();
        pattern2(t, length/random, level-1);
    }
}

public static void pattern(Turtle t, int length){
    for (int i = 0; i < 5; i++) {
        triangle(t, length);
        t.forward(length); 
    } 
}

public static void triangle(Turtle t, int length){
    for (int i = 0; i < 3; i++) {
        t.forward(length);
        t.left(120);
    }
}

Answer 1

The message says when you call pattern(t, length); at line 13 you're passing it a double length when it expects an int length. If you change the pattern and triangle methods to take a double length instead of an int length it will fix the error.

Edit to explicitly explain the error Your methods take an int which can only hold values up to 2^32 - 1 . Doubles can hold values up to ~ 1.7*10^308 (See MAX_VALUE constant in Double class for more exact limit). This means that a double can potentially have values (precision) that would be lost if it was used as an int.

Answer 2

Your length parameter in pattern2() is double. However, in pattern(), length is int. Java would not automatically convert from double to int for you.