CODEWITHSUNDEEP
javainterface
Steeven_b
Steeven_b

Reputation: 777

Java interface, which implementation is called

I have to code a school project, to do that, they gave us some interfaces to help us to design the class implementations.

INode

is one of them :

public interface INode {

void buildString(StringBuilder builder, int tabs);
}

We have to implement this interface several times.

BlockNode

is one of them :

public class BlockNode implements INode {

@Override
public void buildString(StringBuilder builder, int tabs) {
  }
}

Now my problem is that in the main function they do that (the type of parse is INode):

root = parser.parse();
builder = new StringBuilder();
builder.append("PARSE TREE:\n");
root.buildString(builder, 0);

I don't get which implementation of

buildString(StringBuilder builder, int tabs)

is called. It could be the one I wrote above (BlockNode) ? or any other I implemented ? I don't understand which one is called in first..

Upvotes: 0

Views: 156

Answers (2)

msagala25
msagala25

Reputation: 1806

Let's assume we have a Parser Class.

public Parser {
    public INode parse(){
        return new BlockNode(); // this will return a new BlockNode.
    }
}

Now if you want to identify what type would it be to return to you without seeing the parse method. You can change your method in your INode
from:

void buildString(StringBuilder builder, int tabs);

to:

String buildString(StringBuilder builder, int tabs);

and then when you implement it on your class nodes:

public class BlockNode implements INode {
     public String buildString(StringBuilder builder, int tabs) {
          return "BlockNode";
     }
}

or

public class OtherNode implements INode {
     public String buildString(StringBuilder builder, int tabs) {
          return "OtherNode";
     }
}

Now, in this way you can distinguish what type is return by printing it.

root = parser.parse();
builder = new StringBuilder();
builder.append("PARSE TREE:\n");
String nameOfClass = root.buildString(builder, 0);
System.out.println(nameOfClass); // this will identify what type is returned.

Upvotes: 0

zawhtut
zawhtut

Reputation: 8561

- This will invoke method from BlockNode

INode root = parser.parse(); // Let's assume it return new BlockNode();
builder = new StringBuilder();
builder.append("PARSE TREE:\n");
root.buildString(builder, 0);

- This will invoke method from SomeNode

INode root = parser.parse(); // Let's assume it return new SomeNode(); 
builder = new StringBuilder();
builder.append("PARSE TREE:\n");
root.buildString(builder, 0);

Upvotes: 1

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