java.math.BigInteger的用法是否錯誤？

Question

我玩弄java.math.BigInteger。這是我的java類，

public class BigIntegerTest{ 
    public static void main(String[] args) { 
    BigInteger fiveThousand = new BigInteger("5000"); 
    BigInteger fiftyThousand = new BigInteger("50000"); 
    BigInteger fiveHundredThousand = new BigInteger("500000"); 
    BigInteger total = BigInteger.ZERO; 
    total.add(fiveThousand); 
    total.add(fiftyThousand); 
    total.add(fiveHundredThousand); 
    System.out.println(total); 
} 
} 

我認爲結果是555000。但實際是0。爲什麼？

Answer 1

BigInteger對象是不可變的。他們的價值一旦創造就無法改變。

當你調用一個.add新BigInteger的對象被創建並返回，如果您要訪問其值必須存儲。

BigInteger total = BigInteger.ZERO; 
total = total.add(fiveThousand); 
total = total.add(fiftyThousand); 
total = total.add(fiveHundredThousand); 
System.out.println(total); 

（這是精說total = total.add(...)，因爲它只是去除參考老total對象，並重新分配它的參考新一個由.add創建）。

Answer 2

試試這個

BigInteger fiveThousand = new BigInteger("5000"); 
BigInteger fiftyThousand = new BigInteger("50000"); 
BigInteger fiveHundredThousand = new BigInteger("500000"); 
BigInteger total = BigInteger.ZERO; 

total = total.add(fiveThousand).add(fiftyThousand).add(fiveHundredThousand); 
System.out.println(total);