CODEWITHSUNDEEP
java
user3185198
user3185198

Reputation:

Initialize variable inside class without constructor

Here is some simple java code .

class Test {
    public static void main(final String[] args) {
        TestClass c = new TestClass();
        System.out.println(c.x);
    }
}

class TestClass {
    {
        x = 2;
    }
    int x = 1;
}

I am getting the answer 1. Why? Is there no constructor used to initialize?

Upvotes: 4

Views: 1565

Answers (3)

user2700349
user2700349

Reputation:

Because it would be compiled To :

class TestClass {
    int x; 

    TestClass(){
        this.x = 2;
        this.x = 1;
    }
}

Upvotes: 1

Rohit Jain
Rohit Jain

Reputation: 213213

The order of execution of initializer blocks, and variable initializer is specified in JLS § 12.5:

Just before a reference to the newly created object is returned as the result, the indicated constructor is processed to initialize the new object using the following procedure:

[...]

4 Execute the instance initializers and instance variable initializers for this class, assigning the values of instance variable initializers to the corresponding instance variables, in the left-to-right order in which they appear textually in the source code for the class. [..]

So, the initializer blocks and variable initializers executed in order in which they appear in the source file. If you move the variable declaration, int x = 1;, before the initializer block, you'll get the result 2.

Technically, your Test class is compiled to the this:

class TestClass {
    int x;

    public TestClass() {
        super();
        x = 2;
        x = 1;
    }
}

For actual bytecode you can run javap -c command.

Upvotes: 5

RAJIL KV
RAJIL KV

Reputation: 399

TestClass is compiled to be equivalent to this:

class TestClass {
    {
        this.x = 2;
    }

    int x;

    {
        this.x = 1;
    }
}

Upvotes: 6

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