java子字符串无法按预期工作

Question

I'm trying to use substring function in java, but it keeps throwing an error, I want to know why ? the code seems to be good logically speaking but why it is throwing this error

Exception in thread "main" java.lang.StringIndexOutOfBoundsException: String index out of range: -1

What I've read in the documentation substring takes 2 parameter

substring(whereIwantToStart,howManyCharactersToshow)

below is my code

    String test = "160994";
    System.out.println(test.substring(2,1)); //output should be 09 why error?

Can someone explain me what is wrong ? please I need explanation. Thanks :)

Answer 1

See the doc :

public String substring(int beginIndex, int endIndex)

Returns a new string that is a substring of this string. The substring begins at the specified beginIndex and extends to the character at index endIndex - 1. Thus the length of the substring is endIndex-beginIndex.

You need "160994".substring(2, 4) to get 09 .

Answer 2

对于您所需的输出，请使用-

System.out.println(test.substring(2,4)); 

Answer 3

This is the format for the substring in java

public String substring(int beginIndex, int endIndex)

you are specifying start from index 2 and end at index 1 , that's why it's throwing an exception index out of range.

To get the output as 09 you need

 System.out.println(test.substring(2,4));

Appendix - Java Docs https://docs.oracle.com/javase/7/docs/api/java/lang/String.html#substring(int,%20int)

Answer 4

End index should be greater than the Start Index. To get output as '09', you should provide the end index as 4 test.substring(2,4);

Returns a new string that is a substring of this string. The
substring begins at the specified beginIndex and extends to the character at index endIndex - 1 .

Thus the length of the substring is endIndex-beginIndex .

The StringIndexOutOfBoundsException will throw in below cases

1. beginIndex < 0
2. endIndex > value.length
3. endIndex - beginIndex < 0

Answer 5

public String substring(int startIndex, int endIndex) : This method returns new String object containing the substring of the given string from specified startIndex to endIndex.

Let's understand the startIndex and endIndex by the code given below.

String s="hello";  
System.out.println(s.substring(0,2)); 

Output : he

Notice :

endIndex > startIndex

in your case : change between 1 and 2 place to

String test = "160994";
System.out.println(test.substring(2, 4)); //output should be 09

Output : 09

Answer 6

String test = "160994";

System.out.println(test.substring(2,1));

Substring means (beginIndex, endIndex) and endIndex Should be larger than beginIndex.and your value(09) should be stay between beninIndex(which is starting index) and endIndex(Which is last index).

and you have taken endIndex 1 so you are geting the Error because your beginIndex is larger than endIndex.

if you want to get Ans. 09 then you should have to put endIndex 4.

Line will be:-System.out.println(test.substring(2,4));