Java BigInteger add()方法及实例

java.math.BigInteger .add(BigInteger val) 是用来计算两个BigIntegers的算术和。该方法用于对范围远大于java最大数据类型double范围的大数进行算术相加，而不影响结果的精度。该方法对当前的BigInteger进行运算，该方法被调用时，BigInteger作为参数被传递。

语法

public BigInteger add(BigInteger val)

参数： 该方法接受一个参数val，即要添加到这个BigInteger中的值。

返回值： 该方法返回一个BigInteger，该BigInteger持有总和（this + val）。

下面的程序用来说明BigInteger的add()方法。

例1:

// Java program to demonstrate
// add() method of BigInteger
  
import java.math.BigInteger;
  
public class GFG {
    public static void main(String[] args)
    {
        // BigInteger object to store result
        BigInteger sum;
  
        // For user input
        // Use Scanner or BufferedReader
  
        // Two objects of String created
        // Holds the values to calculate the sum
        String input1
            = "5454564684456454684646454545";
        String input2
            = "4256456484464684864864864864";
  
        // Convert the string input to BigInteger
        BigInteger a
            = new BigInteger(input1);
        BigInteger b
            = new BigInteger(input2);
  
        // Using add() method
        sum = a.add(b);
  
        // Display the result in BigInteger
        System.out.println("The sum of\n"
                           + a + " \nand\n" + b + " "
                           + "\nis\n" + sum + "\n");
    }
}

输出。

The sum of
5454564684456454684646454545
and
4256456484464684864864864864
is
9711021168921139549511319409

从上面的例子可以看出，即使添加了长度很大的数字，数据也是完全精确的。

例2:

// Java program to demonstrate
// add() method of BigInteger
  
import java.math.BigInteger;
  
public class GFG {
    public static void main(String[] args)
    {
        // BigInteger object to store result
        BigInteger sum;
  
        // double variable
        // To store result as double
        double d;
  
        // For user input
        // Use Scanner or BufferedReader
  
        // Two objects of String
        // Holds the values to sum
  
        // The number's length is of 400 digits
        // Which is out of range of double
        String input1 = "012345678901234567"
                        + "8901234567890123"
                        + "4567890123456789"
                        + "0123456789012345"
                        + "6789012345678901"
                        + "2345678901234567"
                        + "8901234567890123"
                        + "4567890123456789"
                        + "0123456789012345"
                        + "6789012345678901"
                        + "2345678901234567"
                        + "8901234567890123"
                        + "4567890123456789"
                        + "0123456789012345"
                        + "6789012345678901"
                        + "2345678901234567"
                        + "8901234567890123"
                        + "4554324324362432"
                        + "7674637264783264"
                        + "7832678463726478"
                        + "3264736274673864"
                        + "7364732463546354"
                        + "6354632564532645"
                        + "6325463546536453"
                        + "6546325463546534"
                        + "6325465345326456"
                        + "4635463263453264"
                        + "654632498739473";
        String input2 = "0123456789012345"
                        + "6789012345678901"
                        + "2345678901234567"
                        + "8901234567890123"
                        + "4567890123456789"
                        + "0123456789012345"
                        + "6789012345678901"
                        + "2345678901234567"
                        + "8901234567890123"
                        + "4567890123456789"
                        + "0123456789012345"
                        + "6789012345678901"
                        + "2345678901234567"
                        + "8901234567890123"
                        + "4567890123456789"
                        + "0123456789012345"
                        + "6789012345678901"
                        + "2345873271893718"
                        + "2974897146378481"
                        + "7489127847281478"
                        + "2174871248721847"
                        + "8748327463756475"
                        + "6745781641263981"
                        + "2839721897438974"
                        + "3286574365764576"
                        + "2376914689217817"
                        + "4362473624721647"
                        + "61247612748612746";
  
        // convert the string input to BigInteger
        BigInteger a
            = new BigInteger(input1);
        BigInteger b
            = new BigInteger(input2);
  
        // Using add() method
        sum = a.add(b);
  
        // Display the result in BigInteger
        System.out.println("The sum of\n"
                           + a + " \nand\n" + b + " "
                           + "\nis\n" + sum);
  
        // Using double to hold  the result
        d = Double.parseDouble(sum.toString());
  
        // Display the result in double
        System.out.println("Using double, Sum is "
                           + d);
    }
}

输出。

The sum of
1234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234554324324362432767463726478326478326784637264783264736274673864736473246354635463546325645326456325463546536453654632546354653463254653453264564635463263453264654632498739473
and
1234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234587327189371829748971463784817489127847281478217487124872184787483274637564756745781641263981283972189743897432865743657645762376914689217817436247362472164761247612748612746
is
2469135780246913578024691357802469135780246913578024691357802469135780246913578024691357802469135780246913578024691357802469135780246913578024691357802469135780246913578024691357802469135780246913578024691357802469135780246913578024691357802469135780246913578024691357802469141651513734262516435190263143967454631918743000751861146858652219747883919392209327966909307740297653290433886520376204000415840169342671082000882825735618025902245247352219
Using double, Sum is Infinity

从上面的输出可以看出，使用double来表示更大的整数并不是一个好的选择。
参考： https://docs.oracle.com/en/java/javase/12/docs/api/java.base/java/math/BigInteger.html#add(java.math.BigInteger)