Java String transform to char array

Question

I want to ask how does the "".value transform char array,Thanks

public final class String
implements java.io.Serializable, Comparable<String>, CharSequence {
/** The value is used for character storage. */
private final char value[];

/**
 * Initializes a newly created {@code String} object so that it represents
 * an empty character sequence.  Note that use of this constructor is
 * unnecessary since Strings are immutable.
 */
public String() {
    this.value = "".value;
}

Where did you see this code?

Konstantin Yovkov
– Konstantin Yovkov

2015-09-30 08:04:37 +00:00
Commented Sep 30, 2015 at 8:04 — Konstantin Yovkov
– Konstantin Yovkov, Commented Sep 30, 2015 at 8:04

Holger · Accepted Answer · 2015-09-30 08:21:01Z

4

You should tell, which JRE implementation you are looking at, when you cite its source code.

However, the code is quite simple:

"" refers to a String constant which is initialized by the JVM
since you are inside the String() constructor which may get called by application code, but not JVM internal initialization, it may safely refer to the "" constant
like any other String object, it has the value field, so inside the String constructor, it is no problem to access that private field and copy the reference; it is equivalent to
```
String tmp = "";
this.value = tmp.value;
```

Since both, the "" constant and the instance created with the String() constructor represent empty strings, there is no problem in sharing the char[] array instance between them. However, there are reasons against it:

it is optimizing an uncommon case, as there is usually no reason to ever use the String() constructor at all
it is fragile as it relies on a particular JVM behavior, i.e. that the constant "" is not constructed via the String() constructor; if that assumption is wrong, this implementation will create a circular dependency

answered Sep 30, 2015 at 8:21

Holger

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1 Comment

Risk4U Over a year ago

Thanks a lot for your help

Michal · Accepted Answer · 2015-09-30 08:07:29Z

0

"".value

creates empty char[] array, equivalent of this.value = new char[0];

answered Sep 30, 2015 at 8:07

Michal

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