Tag: 另外

Java中的string和整数的空值

public class Test { public static void main(String[] args) { String s = null; String s1 = null; Integer i = null; Integer i1 = null; System.out.println(s+i); System.out.println(i+s); System.out.println(s+s1); try { System.out.println(i+i1); } catch (NullPointerException np) { System.out.print("NullPointerException"); } } } 问题很简单 – 为什么只在最后一行收到NullPointerException ？