BigDecimal equals() versus compareTo()

问题

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.equals(y));
        System.out.println(x.compareTo(y) == 0 ? \"true\": \"false\");
    }

}

You can (consciously) say that x is equal to y (not object reference), but when you run the program, the following result shows:

false
true

Question: What\'s the difference between compareTo() and equals() in BigDecimal that compareTo can determine that x is equal to y?

PS: I see that BigDecimal has an inflate() method on equals() method. What does inflate() do actually?

回答1:

The answer is in the JavaDoc of the equals() method:

Unlike compareTo, this method considers two BigDecimal objects equal only if they are equal in value and scale (thus 2.0 is not equal to 2.00 when compared by this method).

In other words: equals() checks if the BigDecimal objects are exactly the same in every aspect. compareTo() "only" compares their numeric value.

回答2:

I see that BigDecimal has an inflate() method on equals() method. What does inflate() do actually?

Basically, inflate() calls BigInteger.valueOf(intCompact) if necessary, i.e. it creates the unscaled value that is stored as a BigInteger from long intCompact. If you don't need that BigInteger and the unscaled value fits into a long BigDecimal seems to try to save space as long as possible.

回答3:

You can also compare with double value

BigDecimal a= new BigDecimal("1.1"); BigDecimal b =new BigDecimal("1.1");
System.out.println(a.doubleValue()==b.doubleValue());

来源：https://stackoverflow.com/questions/6787142/bigdecimal-equals-versus-compareto