What does the new Operator and String do in this program?

Question

I am beginner to Java, and I am reading up on Arrays from the tutorial at Oracle.

My question involves this code:

class ArrayCopyDemo {
    public static void main(String[] args) {
        char[] copyFrom = { 'd', 'e', 'c', 'a', 'f', 'f', 'e',
            'i', 'n', 'a', 't', 'e', 'd' };
        char[] copyTo = new char[7];

        System.arraycopy(copyFrom, 2, copyTo, 0, 7);
        System.out.println(new String(copyTo));
    }
}

Specifically,

 System.out.println(new String(copyTo));

What does new String(copyTo) exactly do, or rather why use new and String? What are they doing together? (I understand that they print out "caffein" but only in a very general sense.

It's a constructor call, like any other constructor call. Do you understand constructors in general? String is just the name of a class. — Jon Skeet
– Jon Skeet, Commented Feb 15, 2013 at 16:43
No, I don't think I've seen anything explaining constructors yet. — Ishmael
– Ishmael, Commented Feb 15, 2013 at 16:45
You should probably seek some tutorials on object-oriented programming then. — ajp15243
– ajp15243, Commented Feb 15, 2013 at 16:46
@Chase: Okay, it's probably worth getting hold of a book about Java, or reading up on constructors in the tutorial. — Jon Skeet
– Jon Skeet, Commented Feb 15, 2013 at 16:48

Eng.Fouad · Accepted Answer · 2013-02-15 16:44:16Z

6

The JavaDoc is your friend:

public String(char[] value)

Allocates a new String so that it represents the sequence of characters currently contained in the character array argument. The contents of the character array are copied; subsequent modification of the character array does not affect the newly created string.

Parameters:

value - The initial value of the string

answered Feb 15, 2013 at 16:44

Eng.Fouad

118k75 gold badges326 silver badges431 bronze badges

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

1 Comment

ajp15243 Over a year ago

I wish more people would link to documentation!

PermGenError · Accepted Answer · 2013-02-15 16:44:29Z

2

What does new String(copyTo) exactly do,

It creates a new String object. String class has an Constructor which accepts an char array, which converts the char Array into string literal.

new String(char[] arr) Source

Allocates a new String so that it represents the sequence of characters currently contained in the character array argument. The contents of the character array are copied; subsequent modification of the character array does not affect the newly created string.

answered Feb 15, 2013 at 16:44

PermGenError

46.5k8 gold badges90 silver badges107 bronze badges

Comments

Fritz · Accepted Answer · 2013-02-15 16:45:39Z

0

It creates a new String object containing the text defined by the char array you pass as a parameter. It's just another of the constructors defined in the String class, take a look at it:

public String(char value[]) {
    this.offset = 0;
    this.count = value.length;
    this.value = StringValue.from(value); //returns a copy of the char array
                                          //by using Array.copyOf
}

Aside from looking at the JavaDoc, diging into String's code can help you to comprehend how does it work. this.value is the internal array used to allocate the chars that conform the String.

answered Feb 15, 2013 at 16:45

Fritz

10.1k4 gold badges33 silver badges49 bronze badges

Comments

jhc · Accepted Answer · 2013-02-15 16:50:18Z

0

The function println only accepts the type String. What you have is a char array.

The new keyword indicates that String is a constructor of the class String (as in construction of a new String object).

In the Android Developers site you have a list of all the constructors possible: http://developer.android.com/reference/java/lang/String.html

Specifically, the one you are using is:

String(char[] data)

answered Feb 15, 2013 at 16:50

jhc

1,7694 gold badges24 silver badges47 bronze badges

Collectives™ on Stack Overflow

What does the new Operator and String do in this program?

4 Answers 4

1 Comment

Comments

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

4 Answers 4

1 Comment

Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related