在Java中使用toString（）列出字符串

Question

I'm having ArrayList Contains of String. I would like to check whether the character is present in the arraylist. I'm using the following code.

if(list.toString.contains(char))
{
   // enter code here
}

Can i use this toString() method. What is the drawback?

Answer 1

It would be a really bad idea to use List.toString() and search that. Your code should probably look something like this :

Iterator it = list.getIterator(); 
char searchChar = 'S';

while (it.hasNext())  
{ 
String s = (String) it.next(); 
if ( s.contains(searchChar) ) 
{   
//Found the char! 
} 
}

Answer 2

No you cannot go ahead with arraylist.toString(), as it will not provide string representation of contents in String.

Better approach is to iterate over list and check, as below.

for(String detail:listString){

 if(detail.contains('X')) //replace 'X' with your character
 {
   // do somethng
 }

}    

Answer 3

list.toString() gives you a string representation of a list and thus it contains more characters then just the concatenated list elements

[stringElement1, stringElement2, ... ]

Therefore your approach will not work if the character you are looking for is , , , [ or ] . And keep in mind that this string representation is implementation specific. It might not work for other list implementations than ArrayList

I would recommend to write a method linke this:

private boolean listElementContains(List<String> list, String subString){
    for(String element : list){
        if(element.contains(subString)){
            return true;
        }
    }
    return false;
}

Answer 4

尝试这个，

Arrays.toString(inputList.toArray()).contains(searchValue);

Answer 5

You can call toString() on any Java Object. List is an Object which contains (you guessed it) a list of other Objects. Therefore, you can also call toString() on each Object contained within the List . You should read about inheritance in Java.

In your particular case, you have a List of Strings. What you actually want to do is check each String in the List to see if the String contains a particular character. Topics you may want to read about include iteration, for loops, and for each loops.

Answer 6

If I understand this correctly, your code would look like this:

List<String> strings = new ArrayList<>();
//add strings to list
for (String string : strings) {
    //Look for some character c
    if (string.indexOf(c) >= 0) {
        return true;
    }
}

return false;

On the matter of list.toString , that simply returns a representation of the object as a string; it has nothing to do with the contents. Think of it like a label on a box of stuff that says "Junk." The box is labeled Junk, but you have no idea what's in it.

What's nearly certain is that toString will return a nonsense label for the object in memory. So to get at what's inside, you need to loop through the contents as shown above.

Answer 7

if(list.toString.contains(char))

String 's contains() method won't take char as param , instead check with indexOf

Your code works, with little modifications.

A small example here:

     List<String> list= new ArrayList<>();
     list.add("test");
     list.add("test2");
     if (list.toString().indexOf('t') > -1)      // True
     {
         System.out.println("yes there");
     }

Note:

As a workaround, Make an char array and add your char in to that array and then use contains method.