我不知道如何在Java中进行强制转换

Question

I'm porting some code over from Processing to Java, and one issue I've come across is that processing's precompiler turns any doubles to floats. In Eclipse however, I've had to explicitly cast my values as float. Still though, I get errors that I don't understand. For instance, shouldn't putting an f at the end of this statement fix the type mismatch (Type mismatch: cannot convert from double to float)?

    springing[n] = .05*(.17*(n+1))f; 

And even on simpler statements like this I get a type mismatch. What am I doing wrong?

  float theta = .01f;

Answer 1

Well, your second statement is correct by Java's standards, but in your first example Java is probably trying to prevent you from converting doubles to floats due to a loss of precision that must be explicitly asked for by the programmer, as so:

double a = //some double;
float b = (float) a;  //b will lose some of a's precision

Answer 2

According the Java grammar, the f suffix is only applicable to float literals. Your second statement should work. The first however is an expression and therefore requires a cast:

springing[n] = (float)(.05*(.17*(n+1)));

Answer 3

In your first example, the f suffix is only valid directly on literals, not after a whole expression. So write it in either of those ways (assuming springing is a float[]):

springing[n] = .05f*(.17f*(n+1)); 
springing[n] = (float)( .05*(.17*(n+1)));

The first does the whole calculation (apart from the n+1 part) in float, the second one calculates in double and then converts only the result to float.

(And in both cases, the parenthesis between .05 and .17 (and the matching one) is usually superfluous, since multiplication is associative. It might do some difference for really big values of n , but in these cases you would usually want the other way to avoid overflow.)