Substring in Java - length up to a value

问题

I'm trying to make a substring which lets me have up to 6 letters of a surname, however what I have here seems to throw an error when it finds a surname of less than 6 letters, I have been looking for hours for a solution with no sucess :/

id = firstName.substring (0,1).toLowerCase() + secondName.substring (0,6).toLowerCase();
System.out.print ("Here is your ID number: " + id);

It's the .substring(0,6). I need it to be up to 6 letters not exactly 6.

The error:

Exception in thread "main" java.lang.StringIndexOutOfBoundsException: String index out of range: 6
    at java.lang.String.substring(Unknown Source)
    at Test.main(Test.java:27)

回答1:

Use

secondName.substring (0, Math.min(6, secondName.length()))

回答2:

I prefer

secondName.length > 6 ? secondName.substring(0, 6) : secondName

回答3:

Try the Apache Commons StringUtils class.

// This operation is null safe.
org.apache.commons.lang.StringUtils.substring(secondName, 0, 6);

回答4:

This can be a solution: Check length of surname and decide accordingly

if (secondName.length() >6)
id = firstName.substring (0,1).toLowerCase() + secondName.substring (0,6).toLowerCase(); 
else
id = firstName.substring (0,1).toLowerCase() + secondName.substring (0,secondName.length()).toLowerCase();

System.out.print ("Here is your ID number: " + id);

回答5:

Though you didn't provide the error, it was pretty easy to spot the problem:

 id = firstName.substring (0,1).toLowerCase() + secondName.substring (0,6<secondName.length()?6:secondName.length).toLowerCase();
 System.out.print ("Here is your ID number: " + id);

EDIT This might be more readable:

 id = firstName.substring (0,1).toLowerCase() + (6<secondName.length()?secondName.substring(0,6):secondName).toLowerCase();
 System.out.print ("Here is your ID number: " + id);

回答6:

You'll be getting a java.lang.StringIndexOutOfBoundsException.

You need to make sure the length is always less than the string length. Something like

int len = Math.min(6, secondName.length());
String id = firstName.substring (0,1).toLowerCase() + secondName.substring (0,len).toLowerCase();

来源：https://stackoverflow.com/questions/12955890/substring-in-java-length-up-to-a-value

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java

string

substring