Java字符串之間拼接時，如果有null值，則會直接拼接上null

package com.fgy.demo;

public class demo06 {
    public static void main(String[] args) {
        String str1 = "aaa ";
        String str2 = null;
        String str3 = " bbb";
        System.out.println(str1 + str2 + str3); // aaa null bbb
    }
}

// String源碼
public static String valueOf(Object obj) {
        return (obj == null) ? "null" : obj.toString();
    }