Introduction

~~ I thought it was prepared by the standard method of StringBuilder, but I couldn't find it no matter how I searched, so I made it myself. ~~ ↑ It was a misleading description ...

I wondered if there was a method specializing in erasing the specified number of characters from the end, but I couldn't find it when I searched for it, so I made it myself. is.

Operation check environment

java 1.8.0

Sample source code ①

public class Demo {
    public static void main(String[] args) {
    	StringBuilder sb = new StringBuilder("hoge");

        //Delete one character from the end
    	sb.setLength(sb.length()-1);

        //Execution result: hog
    	System.out.println(sb);
    }
}

setlengthSets the length of the string in the sequence.

length()Returns the current length of the string. In the above example, 4 is returned. All you have to do now is subtract the number of characters you want to delete from ``` length ()` ``.

Note that if you specify a string length less than 0, you will get an error `` `java.lang.StringIndexOutOfBoundsException```.

StringBuilder sb = new StringBuilder("hoge");
sb.setLength(sb.length()-5);
//Error: java.lang.StringIndexOutOfBoundsException: String index out of range: -1

setlengthBefore you dostringbuilderIt may be better to check the length of.

//If n characters or more, delete n characters from the end
if (sb.length() >= n) {
	sb.setLength(sb.length()-n);
}

Sample source code ②

delete(int start, int end)Is the way to use. I told you in the comments.

I first came up with it, but I thought it would be difficult to read because it was necessary to specify both the start position and the end position, so I rejected it. length()I thought I needed to write twice ...

In the first place, if you have length () in a variable, you only have to write it once! Readability isn't bad! I thought again. If there is the character delete, it is easy to understand that the character is deleted.

StringBuilder sb = new StringBuilder("hoge");

int n = 2;              //Number of characters you want to delete from the end
int size = sb.length(); // length()In an int type variable

//Removed two-letter sentence from the end
sb.delete(size-n, size);

//Execution result: ho
System.out.println(sb);

The notes are the same as the sample source code ①, so they are omitted.

Sample source code ③

deletecharat(int index)Is the way to use. I also told you in the comments.

In this case, you can ** delete only one character from the end **. Please note that you cannot delete multiple characters from the end **.

However, I think it is (personally) more readable than the above two sample source codes. I was brilliantly showing the official documentation, but I couldn't notice it at all. So I will mention it in the commandments.

StringBuilder sb = new StringBuilder("hoge");

//Delete one character from the end
sb.deleteCharAt(sb.length()-1);

//Execution result: hog
System.out.println(sb);

At the end

Please let me know if there is a better implementation.

References

StringBuilder (Java Platform SE 8)

[Java] Delete the specified number of characters from the end of StringBuilder