I am trying to parse through a JSON string and convert it to the following POJO:

package apicall;
//POJO representation of OAuthAccessToken
public class OAuthAccessToken {
    private String tokenType;
    private String tokenValue;
    public OAuthAccessToken(String tokenType,String tokenValue) {
        this.tokenType=tokenType;
        this.tokenValue=tokenValue;
    }

    public String toString() {
        return "tokenType="+tokenType+"\ntokenValue="+tokenValue;

    }

    public String getTokenValue() {
        return tokenValue;
    }

    public String getTokenType() {
        return tokenType;
    }

}

In order to do this I have written the following code:

Gson gson=new Gson();
String responseJSONString="{\"access_token\" : \"2YotnFZFEjr1zCsicMWpAA\",\"token_type\" : \"bearer\"}";
OAuthAccessToken token=gson.fromJson(responseJSONString, OAuthAccessToken.class);
System.out.println(token);

When I run the code, I get the following output: tokenType=null tokenValue=null

Instead of tokenType=bearer tokenValue=2YotnFZFEjr1zCsicMWpAA

I dont understand if there's anything I've done wrong. Please help.