如何将 String 转换为 BigInteger？

我试着从标准输入中读取一些非常大的数字，然后把它们加在一起。

但是，要添加到 BigInteger，我需要使用 BigInteger.valueOf(long);:

private BigInteger sum = BigInteger.valueOf(0);


private void sum(String newNumber) {
// BigInteger is immutable, reassign the variable:
sum = sum.add(BigInteger.valueOf(Long.parseLong(newNumber)));
}

这很好，但是由于 BigInteger.valueOf()只接受 long，我不能添加大于 long的最大值(9223372036854775807)的数字。

无论何时尝试添加9223372036854775808或更多，都会出现 NumberFormatException (这是完全可以预料到的)。

有类似 BigInteger.parseBigInteger(String)的东西吗？

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最佳答案

Using the constructor

BigInteger(String val)

Translates the decimal String representation of a BigInteger into a BigInteger.

Javadoc

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According to the documentation:

BigInteger(String val)

Translates the decimal String representation of a BigInteger into a BigInteger.

It means that you can use a String to initialize a BigInteger object, as shown in the following snippet:

sum = sum.add(new BigInteger(newNumber));
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BigInteger has a constructor where you can pass string as an argument.

try below,

private void sum(String newNumber) {
// BigInteger is immutable, reassign the variable:
this.sum = this.sum.add(new BigInteger(newNumber));
}
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Instead of using valueOf(long) and parse(), you can directly use the BigInteger constructor that takes a string argument:

BigInteger numBig = new BigInteger("8599825996872482982482982252524684268426846846846846849848418418414141841841984219848941984218942894298421984286289228927948728929829");

That should give you the desired value.

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For a loop where you want to convert an array of strings to an array of bigIntegers do this:

String[] unsorted = new String[n]; //array of Strings
BigInteger[] series = new BigInteger[n]; //array of BigIntegers


for(int i=0; i<n; i++){
series[i] = new BigInteger(unsorted[i]); //convert String to bigInteger
}
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If you may want to convert plaintext (not just numbers) to a BigInteger you will run into an exception, if you just try to: new BigInteger("not a Number")

In this case you could do it like this way:

public  BigInteger stringToBigInteger(String string){
byte[] asciiCharacters = string.getBytes(StandardCharsets.US_ASCII);
StringBuilder asciiString = new StringBuilder();
for(byte asciiCharacter:asciiCharacters){
asciiString.append(Byte.toString(asciiCharacter));
}
BigInteger bigInteger = new BigInteger(asciiString.toString());
return bigInteger;
}

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