Proj2 Catalog.java

CS61B

Catalog.java

For the first time I used HashMap to store the tables as values using String and Integer as key respectively.

public class Catalog {
    private HashMap<String,Table> nameHash;
    private HashMap<Integer,Table> iDHash;
    public class Table{
        public String tableName;
        public String pkeyFieild;
        public DbFile tableFile;
        public Table(String name, String pkeyFieild, DbFile file){
            this.tableName = name;
            this.pkeyFieild = pkeyFieild;
            this.tableFile = file;
        }
    }
    /**
     * Constructor.
     * Creates a new, empty catalog.
     */
    public Catalog() {
        // some code goes here
        this.nameHash = new HashMap<>();
        this.iDHash = new HashMap<>();
    }

When implementing method like addTable(), I used put() method for HashMap for the fisrt time. Just use hashmap.put(key,value) to put a value to a key in a hashmap.

public void addTable(DbFile file, String name, String pkeyField) {
        // some code goes here
        Table t = new Table(name, pkeyField, file);
        nameHash.put(name,t);
        iDHash.put(file.getId(),t);
    }

When implementing method like getDbFile(int tableid), I used get(key) method for HashMap. Just use hashmap.get(key) then you can get the corresponding value.

public DbFile getDbFile(int tableid) throws NoSuchElementException {
        // some code goes here
        Table tableToGetDbFile = iDHash.get(tableid);
        if(tableToGetDbFile == null){
            throw new NoSuchElementException("the table doesn't exist");
        }else {
            return tableToGetDbFile.tableFile;
        }
    }

When writing tableIdIterator(), things become super easy for HashMap, because the key for HashMap data structure has to be a list or set that are iterable. So I can just return hashmap.keySet().iterator() to get an Iterator of hashmap's keys.

public Iterator<Integer> tableIdIterator() {
        // some code goes here
        Set<Integer> keys = this.iDHash.keySet();
        return keys.iterator();
    }

Finally, there's a clear() method to delete all the info for a hashmap.

  /** Delete all tables from the catalog */
    public void clear() {
        // some code goes here
        this.iDHash.clear();
        this.nameHash.clear();
    }
    }