Exact difference between CharSequence and String in java [duplicate]

by

General differences

There are several classes which implement the CharSequence interface besides String. Among these are

  • StringBuilder for variable-length character sequences which can be modified
  • CharBuffer for fixed-length low-level character sequences which can be modified

Any method which accepts a CharSequence can operate on all of these equally well. Any method which only accepts a String will require conversion. So using CharSequence as an argument type in all the places where you don’t care about the internals is prudent. However you should use String as a return type if you actually return a String, because that avoids possible conversions of returned values if the calling method actually does require a String.

Also note that maps should use String as key type, not CharSequence, as map keys must not change. In other words, sometimes the immutable nature of String is essential.

Specific code snippet

As for the code you pasted: simply compile that, and have a look at the JVM bytecode using javap -v. There you will notice that both obj and str are references to the same constant object. As a String is immutable, this kind of sharing is all right.

The + operator of String is compiled as invocations of various StringBuilder.append calls. So it is equivalent to

System.out.println(
  (new StringBuilder())
  .append("output is : ")
  .append((Object)obj)
  .append(" ")
  .append(str)
  .toString()
)

I must confess I’m a bit surprised that my compiler javac 1.6.0_33 compiles the + obj using StringBuilder.append(Object) instead of StringBuilder.append(CharSequence). The former probably involves a call to the toString() method of the object, whereas the latter should be possible in a more efficient way. On the other hand, String.toString() simply returns the String itself, so there is little penalty there. So StringBuilder.append(String) might be more efficient by about one method invocation.

More Related Contents:

  1. CharSequence VS String in Java?
  2. Why String.replaceAll() in java requires 4 slashes “\\\\” in regex to actually replace “\”?
  3. How to convert a String to CharSequence?
  4. How to convert CharSequence to String?
  5. What’s the best way to check if a String represents an integer in Java?
  6. How to parse a mathematical expression given as a string and return a number? [duplicate]
  7. Regex to match a C-style multiline comment
  8. Does Java have support for multiline strings?
  9. Convert float to String and String to float in Java
  10. How to split a string in Java
  11. Get variable by name from a String
  12. Java – Best way to grab ALL Strings between two Strings? (regex?)
  13. Fast algorithm for searching for substrings in a string
  14. Extracting pairs of words using String.split()
  15. XML Document to String
  16. String replace a Backslash
  17. Converting ArrayList of Characters to a String?
  18. Java String literals concatenation
  19. Can a valid Unicode string contain FFFF? Is Java/CharacterIterator broken?
  20. Display special characters using System.out.println
  21. How do I find out if first character of a string is a number?
  22. In Java, how to find if first character in a string is upper case without regex
  23. Java ‘+’ operator between Arithmetic Add & String concatenation? [duplicate]
  24. How Java do the string concatenation using “+”?
  25. How to convert String object to Boolean Object?
  26. Sort a single String in Java
  27. Java string intern and literal
  28. Java split String performances
  29. Find all words with 3 letters with regex
  30. Parse Date from String in this format : dd/MM/yyyy [to dd/MM/yyyy]

Leave a Comment