package org.scribe.builder.api;

import org.scribe.model.*;
import org.scribe.services.*;

public class YammerApi extends DefaultApi10a
{
  private static final String AUTHORIZATION_URL = "'https://www.yammer.com/oauth/authorize?oauth_token=%s'";

  @Override
  public String getRequestTokenEndpoint()
  {
    return "https://www.yammer.com/oauth/request_token";
  }

  @Override
  public String getAccessTokenEndpoint()
  {
    return "https://www.yammer.com/oauth/access_token";
  }

  @Override
  public String getAuthorizationUrl(Token requestToken)
  {
    return String.format(AUTHORIZATION_URL, requestToken.getToken());
  }

  @Override
  public SignatureService getSignatureService()
  {
    return new PlaintextSignatureService();
  }
}

package org.scribe.builder.api;

import org.scribe.model.*;
import org.scribe.services.*;

public class YammerApi extends DefaultApi10a
{
  private static final String AUTHORIZATION_URL = "https://www.yammer.com/oauth/authorize?oauth_token=%s";

  @Override
  public String getRequestTokenEndpoint()
  {
    return "https://www.yammer.com/oauth/request_token";
  }

  @Override
  public String getAccessTokenEndpoint()
  {
    return "https://www.yammer.com/oauth/access_token";
  }

  @Override
  public String getAuthorizationUrl(Token requestToken)
  {
    return String.format(AUTHORIZATION_URL, requestToken.getToken());
  }

  @Override
  public SignatureService getSignatureService()
  {
    return new PlaintextSignatureService();
  }
}

Remove Single-Quatation from AUTHORIZATION_URL