BigInteger ​

In Java, the maximum range of integers provided natively by the CPU is a 64-bit long integer. Using long integers can be calculated directly through CPU instructions, which is very fast.

What if the range of integers we use exceeds long type? At this time, you can only use software to simulate a large integer. java.math.BigInteger is used to represent integers of any size. BigInteger internally uses an int[] array to simulate a very large integer:

BigInteger bi = new BigInteger("1234567890");
System.out.println(bi.pow(5)); // 2867971860299718107233761438093672048294900000

When performing operations on BigInteger , you can only use instance methods, for example, addition:

BigInteger i1 = new BigInteger("1234567890");
BigInteger i2 = new BigInteger("12345678901234567890");
BigInteger sum = i1.add(i2); // 12345678902469135780

Compared with long integer operations, BigInteger does not have range restrictions, but the disadvantage is that it is slower.

You can also convert BigInteger to long type:

BigInteger i = new BigInteger("123456789000");
System.out.println(i.longValue()); // 123456789000
System.out.println(i.multiply(i).longValueExact()); // java.lang.ArithmeticException: BigInteger out of long range

When using the longValueExact() method, if it exceeds the range of the long type, ArithmeticException will be thrown.

BigInteger , like Integer and Long , is also an immutable class and also inherits from the Number class. Because Number defines several methods for conversion to basic types:

• Convert to byte : byteValue()
• Convert to short : shortValue()
• Convert to int : intValue()
• Convert to long : longValue()
• Convert to float : floatValue()
• Convert to double : doubleValue()

Therefore, through the above method, BigInteger can be converted into a basic type. If the range represented by BigInteger exceeds the range of the basic type, the high-order information will be lost during conversion, that is, the result may not be accurate.

If you need to accurately convert to a basic type, you can use intValueExact() , longValueExact() and other methods. If it goes out of range during conversion, ArithmeticException will be thrown directly.

If the value of BigInteger even exceeds the maximum range of float (3.4x10 38 ), what is the returned float?

// BigInteger to float
import java.math.BigInteger;

public class Main {
    public static void main(String[] args) {
        BigInteger n = new BigInteger("999999").pow(99);
        float f = n.floatValue();
        System.out.println(f); // Infinity
    }
}

Summary ​

BigInteger is used to represent integers of any size;

BigInteger is an immutable class and inherits from Number ;

When converting BigInteger into a basic type, you can use methods such as longValueExact() to ensure accurate results.