symbol.java

java语言开发的基于tiny语言的编译器

package jeex.tiny;
import java.util.*;
/**
 * Attributes of an identifier are hold in a symbol.
 */
class Symbol {
	/**
	 * Memory address of this identifier.
	 */
	int address;
	/**
	 * Identifier name this symbol corespondent to.
	 */
	String name;
	/**
	 * Only can be created in enter().
	 */
	private Symbol(String name,int address) {
		this.name = name;
		this.address = address;
	}
	
	public String toString() {
		return name + ":" + address;
	}
	/**
	 * Create a symbol and put the symbol into symbol table.
	 * @param name - name of identifier
	 */
	static Symbol enter(String name) {
		Symbol s = new Symbol(name,offset++);
		symtab.put(name,s);
		return s;
	}
	/**
	 * Returns a defined symbol. If not defined, return null.
	 * @param name - name of identifier
	 */
	static Symbol get(String name) {
		return (Symbol)symtab.get(name);
	}
	/**
	 * Returns true if the name is entered in the symbol table.
	 */
	static boolean isDefined(String name) {
		return symtab.containsKey(name);
	}
	/**
	 * Symbol table.
	 */
	static Map symtab = new HashMap();
	/**
	 * Next created symbol's address, updated when a new symbol created in enter().
	 */
	static int offset = 0;
}