how does stringbuffer/stringbuilder works in memory? how does the stringbuilder.delete function works?

Question

I have appended some strBuild with some characters and putting that strBuild into stringBuildArr. then called the java.lang.StringBuilder.delete(int start, int end) function on strBuild.

Here is the issue not only this deletes the data from strBuild but also from stringBuildArr.

    StringBuilder strBuild = new StringBuilder();
    StringBuilder stringBuildArr[] = new StringBuilder[10];
    strBuild.append("hgfd");
    stringBuildArr[0] = strBuild;
    System.out.println("Output1: "+stringBuildArr[0]);
    strBuild.delete(0, strBuild.length());
    System.out.println("Output2: "+stringBuildArr[0]);

RESULT

Output1: hgfd

Output2:

so, how does storage of these stringbuilder and stringbuffer class works?

Elliott Frisch · Accepted Answer · 2019-11-18 06:03:14Z

1

There is no "issue" here, the array stores a reference to the same strBuild instance; there is no copy with stringBuildArr[0] = strBuild; because copying the StringBuilder is not free. But if you want a copy that is easy enough, change it to

stringBuildArr[0] = new StringBuilder(strBuild);

answered Nov 18, 2019 at 6:03

Elliott Frisch

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3 Comments

vaibhavcool20 Over a year ago

i named it an issue for lack of better word. what does this "because copying the StringBuilder is not free" mean?

Shankar Saran Singh Over a year ago

@elliot, seems like he was not sure how to ask or how to mention, he is new.

Elliott Frisch Over a year ago

@vaibhavcool20 It means creating a unique reference copy of the StringBuilder instance requires a copy operation which is not required in all cases. In short, TANSTAAFL

SuleymanSah · Accepted Answer · 2019-11-18 06:27:32Z

1

The Java StringBuilder is a class that most Java programmers are familiar with. Strings are immutable, so every change in a string will cause a new object created however in StringBuilder or buffer, it is mutable. This means it will work on the same object, so deleting will delete the content and hence all reference pointing to the same object will have the same behaviour.

For more info check out the official documentation: Java Docs

edited Nov 18, 2019 at 6:27

SuleymanSah

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answered Nov 18, 2019 at 6:05

Shankar Saran Singh

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2 Comments

vaibhavcool20 Over a year ago

so, when i call this ` stringBuildArr[0] = strBuild;` only reference is shared not its content?.

Shankar Saran Singh Over a year ago

@vaibhavcool20 , Yea logically you can say that. It's better to go through with the official link I shared, it will remove all your doubts. String concept is very wide and in Java world one should be very clear to that. Happy coding, accept the answer if you are clear, it will help others

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