The output from the following code is 123 because substring takes from beginIndex to EndIndex - 1. However, I am surprised how char here is understood as 3 (int) because substring take two ints. What is the concept behind this?
String x = "12345";
char a = 3;
x = x.substring(0, a);
System.out.println(x);
推薦答案
這可以追溯到 C，其中 char 本質上是一種窄整數類型，并在必要時隱式轉換為 int.
This goes all the way back to C, where char is in essence a narrow integer type and gets implicitly converted to int whenever necessary.
在 Java 中，這在技術上稱為擴展原語轉換"，并在 JLS 的第 5.1.2 節.
In Java, this is technically known as a "widening primitive conversion", and is covered in section 5.1.2 of the JLS.
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