code: package operators;
  
  public enum PropositionalLogicOperator {
  	AND("&&"), OR("||"), NOT("!");
  
  	private final String operaor;
  
  	private PropositionalLogicOperator(String operator) {
  		this.operaor = operator;
  	}
  
  	public String toString() {
  		return this.operaor;
  	}
  	
  	public static PropositionalLogicOperator parse(String value){
  		switch(value){
  			case "&&": return PropositionalLogicOperator.AND;
  			case "||": return PropositionalLogicOperator.OR;
  			case "!": return PropositionalLogicOperator.NOT;
  			default:
  				throw new IllegalArgumentException("Operator "+value+" not present");
  		}
  	}
  }