JsonValue avoiding casting.

Example.java

import static JsonUtil.match;
public class Example {
  class Pojo {
    String field1;
    int field2;
  }
  public Pojo toPojo(JsonValue val) {
    return match(val, new JsonMatch<Pojo>() {
      public Pojo matchDefault() {
        return null;
      }
      public Pojo match(JsonObject obj) {
        Pojo pojo = new Pojo();
        pojo.field1 = match(obj.get("field1"), new JsonMatch<String>() {
          public String matchDefault() {
            return null;
          }
          public String match(String str) {
            return str;
          }
        });
        pojo.field2 = match(obj.get("field2"), new JsonMatchInt() {
          public int matchDefault() {
            return 0;
          }
          public int match(JsonNumber num) {
            return num.intValue();
          }
        });
      }
    });
  }

JsonMatch.java

interface JsonMatch<T> {
    default T match(String str) {
      return matchDefault();
    }
    default T match(JsonObject obj) {
      return matchDefault();
    }
    default T match(JsonArray arr) {
      return matchDefault();
    }
    default T match(JsonNumber num) {
      return matchDefault();
    }
    default T match(boolean bool) {
      return matchDefault();
    }
    default T matchNull() {
      return matchDefault();
    }
    T matchDefault();
}

JsonMatchInt.java

interface JsonMatchInt {
    default int match(String str) {
      return matchDefault();
    }
    default int match(JsonObject obj) {
      return matchDefault();
    }
    default int match(JsonArray arr) {
      return matchDefault();
    }
    default int match(JsonNumber num) {
      return matchDefault();
    }
    default int match(boolean bool) {
      return matchDefault();
    }
    default int matchNull() {
      return matchDefault();
    }
    int matchDefault();
}

JsonUtils.java

public class JsonUtils {
  public <T> T match(JsonValue value, JsonMatch<T> switcher) {
    if (null == value || JsonValue.NULL == value) {
      return switcher.matchNull();
    } else if (JsonValue.TRUE == value) {
      return switcher.match(true);
    } else if (JsonValue.FALSE == value) {
      return switcher.match(false);
    } else if (value instanceof JsonObject) {
      return switcher.match((JsonObject)value);
    } else if (value instanceof JsonArray) {
      return switcher.match((JsonArray)value);
    } else if (value instanceof JsonNumber) {
      return switcher.match((JsonNumber)value);
    } else if (value instanceof JsonString) {
      return switcher.match((JsonString)value);
    }
    throw new IllegalStateException("Unexpected JsonValue subtype " + value.getClass());
  }
  // TODO: Add "primitive" versions for ALL types to avoid auto/boxing and unboxing.
  public int match(JsonValue value, JsonMatchInt switcher) {
    if (null == value || JsonValue.NULL == value) {
      return switcher.matchNull();
    } else if (JsonValue.TRUE == value) {
      return switcher.match(true);
    } else if (JsonValue.FALSE == value) {
      return switcher.match(false);
    } else if (value instanceof JsonObject) {
      return switcher.match((JsonObject)value);
    } else if (value instanceof JsonArray) {
      return switcher.match((JsonArray)value);
    } else if (value instanceof JsonNumber) {
      return switcher.match((JsonNumber)value);
    } else if (value instanceof JsonString) {
      return switcher.match((JsonString)value);
    }
    throw new IllegalStateException("Unexpected JsonValue subtype " + value.getClass());
  }
  
}