CODEWITHSUNDEEP
javastring
Kirill
Kirill

Reputation: 6036

String class value variable used in equals() method: how and when is it defined?

I have investigated equals() method in String class and found that it uses value - an array of chars. Here this variable is: 

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

    ...
}

As a string is created then this value is immediately defined and seen in a debug mode. However I do not find a place where this value is defined.

My question. When we are creating a string like this:

String str = "My string";

how and when this value is defined?

Edit: I have seen 3 constructors that @xenteros mentioned. However this.value is defined as an array of chars only in the last constructor. Directly I am not invoking it. Also if you set breakpoints in these constructors it will not stop there.

Upvotes: 0

Views: 64

Answers (1)

xenteros
xenteros

Reputation: 15852

value is initialized in each constructor.

public String() {
    this.value = new char[0];
}

public String(String original) {
    this.value = original.value;
    this.hash = original.hash;
}

public String(char value[]) {
    this.value = Arrays.copyOf(value, value.length);
}

source code for String.java

When you execute

String str = "My string";

there is no magic happening. JVM creates new String calling a constructor. It's explained in the language specification

Edit:

In the JVM available in OpenJDK the following file contains the native code in which String literals are created. It's done in C++, so no Java constructors are called.

Link

Upvotes: 2

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