java Object t 强转String

Object reallyAString = "foo";

String str = (String) reallyAString;

Object reallyAString = "foo";

String str = reallyAString.toString();

Object reallyAString = "foo";

String str = String.valueOf(reallyAString);

源码分析：

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

与object.toString()不同的是，如果被转换对象为null时，String.valueOf()不会抛出空指针异常，而是转换为字符串”null”. 
如果被转换对象不为null，则直接调用被转换对象的toString().