public class SchemaGlobalDescribe{
    //idをもとに、オブジェクトAPI名を取得
    public static String findObjectNameFromRecordIdPrefix(String recordIdOrPrefix){
        String objectName = '';
        try{
            String myIdPrefix = String.valueOf(recordIdOrPrefix).substring(0,3);
            Map<String, Schema.SObjectType> gd =  Schema.getGlobalDescribe(); 
            for(Schema.SObjectType stype : gd.values()){
                Schema.DescribeSObjectResult r = stype.getDescribe();
                String prefix = r.getKeyPrefix();
                if(prefix!=null && prefix.equals(myIdPrefix)){
                    objectName = r.getName();
                    break;
                }
            }
        }catch(Exception e){
            System.debug(e);
            System.debug(Logginglevel.ERROR, e.getStackTraceString());
        }
        return objectName;
    }
}