Analysis of Java large number BigInteger and BigDecimal class examples

BigInteger Class

In Java, there are many classes that need to be processed, such as the Integer class, but the Integer class also has an upper limit. Its maximum value is 2^31-1.

If we want to represent a larger number at this time, it cannot be represented by Integer, so Java provides the BigInteger class.

The numbers supported by the BigInteger class can be said to be infinite, and it supports integers of arbitrary precision, which means that it can accurately represent any value without loss.

I would also like to emphasize here that because the number type passed in is a character type, you cannot use - * /

corresponding to the method of using them when doing operations:

add(), subtract(), multiply(), divide()

There are also some common methods:

equals method. Compare

Code demonstration:

import java.math.BigInteger;
public class Demo01 {
    public static void main(String[] args) {
        BigInteger bigInteger1 = new BigInteger("2222222222222222222222222222222");
        BigInteger bigInteger2 = new BigInteger("1111111111111111111111111111111");
        System.out.println("bigInteger1大数为：" + bigInteger1);
        System.out.println("bigInteger2大数为：" + bigInteger2);
        System.out.println("两个大数相加：" + bigInteger1.add(bigInteger2));//加
        System.out.println("两个大数相减：" + bigInteger1.subtract(bigInteger2));//减
        System.out.println("两个大数相乘：" + bigInteger1.multiply(bigInteger2));//乘
        System.out.println("两个大数相除：" + bigInteger1.divide(bigInteger2));//除
        System.out.println("两个大数相比：" + bigInteger1.equals(bigInteger2));//equals进行比较
    }
}

When doing division, if there are decimal places, the decimal places are intercepted here.

Of course, there are not only integer types, but also floating point types.

BigDecimal Class

Of course, the precision of the floating point type can also be as large as possible.

import java.math.BigDecimal;
public class Demo02 {
    public static void main(String[] args) {
        BigDecimal bigDecimal1 = new BigDecimal("12232423432432.53241234324");
        BigDecimal bigDecimal2 = new BigDecimal("2.0");
        System.out.println("bigDecimal1值： " + bigDecimal1);
        System.out.println("bigDecimal2值： " + bigDecimal2);
        System.out.println("加：" + bigDecimal1.add(bigDecimal2));
        System.out.println("减：" + bigDecimal1.subtract(bigDecimal2));
        System.out.println("乘：" + bigDecimal1.multiply(bigDecimal2));
        System.out.println("除：" + bigDecimal1.divide(bigDecimal2));
    }
}

In the BigDecimal method, it can also better solve the accuracy problem in the Java language (such as the problem that the result of 0.1x3 == 0.3 is false)

The problem of incomplete division in the BigDecimal class

But there is also a point that needs to be paid attention to when using BigDecimal (when it encounters a problem that cannot be divided, it will Choose the one that reports an error.)

So when doing division, just give it a truncation number.

Let’s look at a method first:

public BigDecimal divide(BigDecimal divisor, int scale, int roundingMode)

divisor - divisor.

scale - How many digits to keep after the decimal point

roundingMode - Select the rounding mode

So we can write it like this:

Rounding mode selection:

Mode	Meaning
ROUND_CEILING	Get the number towards positive infinity
ROUND_DOWN	Get the number towards 0
ROUND_FLOOR	Take the number toward negative infinity
ROUND_HALF_DOWN	Round down when encountering .5
ROUND_HALF_UP	Rounding up when encountering .5
ROUND_HALF_EVEN	Rounding up when encountering 5, look at the previous number, greater than 5 upwards, less than 5 upwards Down, equal to 5 and look forward.

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