Why are numbers with a leading sign (plus or minus) when converted to BigDecimal, treated as valid numbers in Java?

Question

The following expressions are valid in Java as obvious

int a = -0;
int b = +0;

and so are the following.

Integer c = new Integer(-0);
int d = Integer.parseInt("-0");
BigDecimal e = new BigDecimal("-0");

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The following statements are however invalid.

Integer f = new Integer("+0");   //Leading + sign.
int g=Integer.parseInt("+0");    //Leading + sign.

Both of them throw the NumberFormatException.

The following statement with BigDecimal however compiles and runs without causing an exception to be thrown.

BigDecimal bigDecimal = new BigDecimal("+0");  //Leading + sign.

Why is a leading + sign valid with BigDecimal here which however doesn't appear to be the case with the other datatypes available in Java?

Answer 1

According to the documentation, negative signs needs the minus sign. But if its a positive Integer, no need for a plus sign.

public static int parseInt(String s)

The characters in the string must all be decimal digits, except that the first character may be an ASCII minus sign '-' ('\u002D') to indicate a negative value. The resulting integer value is returned, exactly as if the argument and the radix 10 were given as arguments to the parseInt(java.lang.String, int) method.

Then for the constructor:

public Integer(String s)

The string is converted to an int value in exactly the manner used by the parseInt method for radix 10.