Several methods of converting object to string

1.object.toString() Method

    This method should pay attention to object Not for null, Otherwise it will be reported NullPointException, Don't use this method in general .

2.String.valueOf(object) Method

    There is no need to worry about this method object by null The problem of , if nul

l, It will be converted to "null" character string , instead of null. Special attention should be paid to this point ."null" and null It's not a concept .

3.(String)(object) Method

    There is no need to worry about this method object by null The problem of . however ,object If it can be converted to String The object of . if Object object = 1, Again (String)1, Class conversion exception will be reported .

4.“”+object Method

    There is no need to worry about this method object by null The problem of . But if object by null, Returns the "null" character string , and String.valueOf(object) equally .
 

The following is a code example ：

 
 
public class Test {
 
	public static void main(String[] args) {
		Object object = null;
		System.out.println("(String)null and \"null\" The result of the comparison is ：" + ("null".equals((String)object)));
		System.out.println("String.valueOf(null) and \"null\" The result of the comparison is ：" + "null".equals(String.valueOf(object)));
		System.out.println("(\"\" + null) and \"null\" The result of the comparison is ：" + "null".equals("" + object));
	}
}

Running results ：

              (String)null and "null" The result of the comparison is ：false
  String.valueOf(null) and "null" The result of the comparison is ：true
                ("" + null) and "null" The result of the comparison is ：true

The way	Example	matters needing attention
Object.toString()	Object object = getObject(); System.out.println(object.toString());	Pay attention when using , Must ensure object No null value , Otherwise, it will throw NullPointerException abnormal .
(String)obj	Object obj = new Object (); String strVal = (String)obj;	The converted data type must be converted to String type . So it's best to use it  instanceof  Do a type check , To see if it can be converted . Otherwise, it's easy to throw CalssCastException abnormal . Besides , The reason to be particularly careful is defined as Object Objects of type are being converted to String Grammar checking does not report errors , This can lead to potential errors , in addition , because null Value can be cast to any java Class types ,(String)null It's also legal .
String.valueOf(Object)	String.valueOf(object)	Pay attention to when object by null when ,String.valueOf(object) The value of is a string "null", instead of null, It is equivalent to displaying the empty flag as data .