java Float: == equals compareTo

java equals compareto
user1703055 picture user1703055 · Oct 25, 2012 · Viewed 7.7k times · Source

I have 2 questions.

1) I was told that when comparing two Float or Double data, use compareTo instead of equals. I don't know the reason. Is there any example that shows where using equals will lead something wrong?

2) See this code:

  float f2=(float)1.123450;
  Float f3=new Float(1.123450);

  System.out.println(f3==f2);   // result is true

I think using == means the two data point to the same memory address. But do f3 and f2 have the same address? Doesn't new Float(...) create a new space?

Answer

Ted Hopp picture Ted Hopp · Oct 25, 2012

If both arguments were reference types, then == would test memory locations. However, if one of the arguments to == (or !=) is numeric and the other is convertible to numeric (using unboxing), then the comparison is done by comparing numerical values after unboxing. So the comparison in this case is done on the basis of the floating point values (which in this case are identical). See the Java Language Specification §15.21.1 for details.

Note, however, that Float.NaN == Float.NaN is false.

Related questions

compareTo() vs. equals()

When testing for equality of String's in Java I have always used equals() because to me this seems to be the most natural method for it. After all, its name already says what it is intended to do. However, a …

Read More
BigDecimal equals() versus compareTo()

Consider the simple test class: import java.math.BigDecimal; /** * @author The Elite Gentleman * */ public class Main { /** * @param args */ public static void main(String[] args) { // TODO Auto-generated method stub BigDecimal x = new BigDecimal("1"); BigDecimal y = new BigDecimal("1.00"); System.out.println(x.…

Read More
How does compareTo work?

I know that compareTo returns a negative or positive result on how well one string correlates to the other, but then why: public class Test { public static void main(String[] args) { String y = "ab2"; if(y.compareTo("ac3") == -1) { System.…

Read More