如何在Java中比较String和BigInteger之间的值

Question

String str="1234";
String str2="1234";
BigInteger bigInt=new BigInteger("1234");
Object v1=str;
Object v2=str2;
Object v3=bigInt;
System.out.println("Condition1==>>"+v1.equals(v2));
System.out.println("Condition2==>>"+v1.equals(v3));`

Output:

Condition1==>>true

Condition2==>>false

Why the second condition( v1.equals(v3) ) result is false even though the values are same?.What is the difference between two conditions? How to make the second condition result to true?

Answer 1

You might be confused about how types work. Sometimes, there are certain similar (isomporphic) values between two types. For example, the String "123" and the int 123 . Although they look the same, and can be converted from one to the other without loss of information, they aren't actually the same type (and they have no pre-defined automatic conversion in Java), therefore no two values from each type will be equal.

You have to define and perform those conversions yourself. So you'd need to write:

new BigInteger(v1).equals(v3)

Answer 2

You need to apply equals on the same class objects. So you need to compare String and String or BigInteger and BigInteger . You can get the String value of your BigInteger and compare it with the String or you need to create a new BigInteger from the String and compare it with the other String .

Answer 3

As @RohitJain commented They are not even the same type. Actually the first check in every equals() method is

if(other instanceof ThisType)

In your case:

bigInt.toString().equals(str1)

would return true.