Java compare integer and bigInteger

问题

How do I compare an int with a BigInteger in Java? I specifically need the know if an int is less than a BigInteger. Here is the code I am using:

private static BigInteger two = new BigInteger("2");
private static BigInteger three = new BigInteger("3");
private static BigInteger zero = new BigInteger("0");    
public static BigInteger bigIntSqRootCeil(BigInteger x) throws IllegalArgumentException {
    if (x.compareTo(BigInteger.ZERO) < 0) {
        throw new IllegalArgumentException("Negative argument.");
    }
    if (x == BigInteger.ZERO || x == BigInteger.ONE) {
        return x;
    }
    BigInteger two = BigInteger.valueOf(2L);
    BigInteger y;
    for (y = x.divide(two);
            y.compareTo(x.divide(y)) > 0;
            y = ((x.divide(y)).add(y)).divide(two));
    if (x.compareTo(y.multiply(y)) == 0) {
        return y;
    } else {
        return y.add(BigInteger.ONE);
    }
}
private static boolean isPrimeBig(BigInteger n){
    if (n.mod(two) == zero)
        return (n.equals(two));
    if (n.mod(three) == zero)
        return (n.equals(three));
    BigInteger m = bigIntSqRootCeil(n);
    for (int i = 5; i <= m; i += 6) {
        if (n.mod(BigInteger.valueOf(i)) == zero)
            return false;
        if(n.mod(BigInteger.valueOf(i + 2)) == zero)
            return false;
    };
    return true;
};

Thanks.

回答1:

How do I compare an int with a BigInteger in Java? I specifically need the know if an int is less than a BigInteger.

Turn the int into a BigInteger before comparing:

if (BigInteger.valueOf(intValue).compareTo(bigIntegerValue) < 0) {
  // intValue is less than bigIntegerValue
}

回答2:

Instead of

if (x == BigInteger.ZERO || x == BigInteger.ONE) {
    return x;

You should use :-

if (x.equals(BigInteger.ZERO) || x.equals(BigInteger.ONE)){
return x;

Also, you should change the Integer first to BigInteger, and then compare, as mentioned by Joe in his answer:

 Integer a=3;
 if(BigInteger.valueOf(a).compareTo(BigInteger.TEN)<0){
    // your code...
 }
 else{
    // your rest code, and so on.
 }

回答3:

Just use BigInteger.compare:

int myInt = ...;
BigInteger myBigInt = ...;
BigInteger myIntAsABigInt = new BigInteger(String.valueOf(myInt));

if (myBigInt.compareTo(myIntAsABigInt) < 0) {
    System.out.println ("myInt is bigger than myBigInt");
} else if (myBigInt.compareTo(myIntAsABigInt) > 0) {
    System.out.println ("myBigInt is bigger than myInt");
} else {
    System.out.println ("myBigInt is equal to myInt");
}

来源：https://stackoverflow.com/questions/25824764/java-compare-integer-and-biginteger

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java

biginteger

bigint