A simple json parser created as part the https://codingchallenges.fyi/challenges/challenge-json-parser by John Crickett.

The parser uses a Deque as the LIFO data structure for remembering the previous state. A JsonNode is an interface as below.

public interface JsonNode {
    public int getDepth();
    public void setDepth(int depth);
    public boolean isArray();
    public boolean isElement();
    public int getIndex();
    public void setIndex(int index);
}

The interface is implemented by the following concrete classes. (The class code is truncated for brevity here).

1. JsonElement - Represents the json syntactical tokens( { } [ ] , : etc), simple string or number literals.

public class JsonElement implements JsonNode {
    private String data;
    private JsonSymbol symbol;
    private int index;
}

2. JsonObject - Represents a json object which can have key-value pairs.

public class JsonObject extends HashMap<String, JsonNode> implements JsonNode {
    private int index;
    private int depth;
}

3. JsonArray - Represents a json array which can list of values(may be json objects, jsonarrays or simple tokens).

public class JsonArray extends ArrayList<JsonNode> implements JsonNode {
    private int index;
    private int depth;
}

The following image represents how the parsing is achieved for a simple json {"key":"value"}