Usage StringBuffer and String?

Question

As known String is immutable in Java. I have the following method's body which return String:

Partner partner = context.getComponent(ComponentNames.PARTNER_COMPONENT_NAME);
String lastAccesDate = partner.getLastAccessDate();
if(lastAccesDate == null) {
    return "";
}
lastAccesDate = new SimpleDateFormat(DATE_PATTERN).format(); //1
return lastAccesDate;

The thing is because of string immutability, a new String object will be created at //1, so actually I'll have two String Objects, the first one contains partner.getLastAccessDate();, the second one new SimpleDateFormat(DATE_PATTERN).format();. The overhead is not good, how can I avoid it?

@Sharpedge Why don't a StringBuffer? One's mutable, so we can modify the string it contains. — St.Antario
– St.Antario, Commented Dec 24, 2014 at 11:20
from java docs "Every string buffer has a capacity. As long as the length of the character sequence contained in the string buffer does not exceed the capacity, it is not necessary to allocate a new internal buffer array. If the internal buffer overflows, it is automatically made larger. As of release JDK 5, this class has been supplemented with an equivalent class designed for use by a single thread, StringBuilder. The StringBuilder class should generally be used in preference to this one, as it supports all of the same operations but it is faster, as it performs no synchronization." — Sharp Edge
– Sharp Edge, Commented Dec 24, 2014 at 11:22
What does lastAccesDate = new SimpleDateFormat(DATE_PATTERN).format(); do? The format method must have a Date as an argument. Also, although it is true that a new String is created when using the format (I looked at the Java source code) this is not because of String immutability, but despite immutability. It is theoretically possible that the format method would call String.intern(String) in order to save memory since the String cannot be changed anyway. — Joseph K. Strauss
– Joseph K. Strauss, Commented Dec 24, 2014 at 12:46

sol4me · Accepted Answer · 2014-12-24 11:21:47Z

1

Use StringBuffer in case of multithreading(i.e. if you need a thread-safe, mutable sequence of character) otherwise use StringBuilder

answered Dec 24, 2014 at 11:21

sol4me

15.8k6 gold badges37 silver badges35 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

St.Antario Over a year ago

This method is from the web application, so I do use StringBuffer, don't I?

sol4me Over a year ago

@St.Antario it depends if you are creating the Object inside the method something like public void foo() {StringBuilder sb=//....} then StringBuilder is the choice to go because the object will be created on stack and every thread will have it own so no problem. But if you need to declare the object outside the method i.e. on the heap then StringBuffer is must

Abhishek Goswami · Accepted Answer · 2014-12-24 11:26:19Z

0

see when you assign second time string to the String object lastAccessDate, there is no overhead as automaticaly garbage collector will free the space which occupied by first object because no object has reference to the same. so no need to worry about overhead

answered Dec 24, 2014 at 11:26

Abhishek Goswami

411 silver badge3 bronze badges

Collectives™ on Stack Overflow

Usage StringBuffer and String?

2 Answers 2

2 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

2 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related