Parse Tree Expression to List of expressions in Java

Question

I have tree with Expressions(odata4j). I need to parse it to list of Expressions like in botton on photo below:

Every OrExpression and AndExpression has methods like getRHS(right) and getLeft(left) to get objects below.

Till now I have the following code:

private BinaryCommonExpression getLeftRek(BinaryCommonExpression expr, ConditionOperator conditionOperator) {

    BinaryCommonExpression lhs = expr;
    if (lhs.getLHS() instanceof EntitySimpleProperty == false) {
        if(lhs instanceof AndExpression){
            conditionOperator = ConditionOperator.AND;
        }else if(lhs instanceof OrExpression){
            conditionOperator = ConditionOperator.OR;
        }
        getLeftRek((BinaryCommonExpression)lhs.getLHS(), conditionOperator);
        if(lhs.getRHS() instanceof StringLiteral == false && lhs.getRHS() instanceof DateTimeLiteral == false && lhs.getRHS() instanceof IntegralLiteral == false/*lhs.getRHS() instanceof AndExpression || lhs.getRHS() instanceof OrExpression*/){
            getLeftRek((BinaryCommonExpression)lhs.getRHS(), null);
        }
    } else {
        Criterion lhsFinish = getLHSFinish(lhs, conditionOperator);
        stack.push(lhs+ " "+conditionOperator); 
    }
    return lhs;
}

Here is result of my list:

[EqExpression(1) OR, EqExpression(2) AND, LtExpression(3) null, LtExpression(4) OR, EqExpression(5) null]

I can't get operator to LtExpression(3) and EqExpression(5) because its 2 levels higher in tree.

Any ideas?

Answer 1

I made it by stack.

stack.push(lhs);
    while(stack.get(stack.size()-1) instanceof OrExpression || stack.get(stack.size()-1) instanceof AndExpression){

        BinaryCommonExpression popValue = (BinaryCommonExpression)stack.pop();

        try{
            if(stack.get(stack.size()-2) instanceof OrExpression || stack.get(stack.size()-2) instanceof AndExpression){
                String operatorAfter = (String)stack.pop();
                BinaryCommonExpression popVal2 = (BinaryCommonExpression)stack.pop();
                BinaryCommonExpression lhs2 = (BinaryCommonExpression)popVal2.getLHS();
                BinaryCommonExpression rhs = (BinaryCommonExpression)popVal2.getRHS();
                stack.push(lhs2);
                if(popVal2 instanceof OrExpression){
                    stack.push("OR");
                }else if (popVal2 instanceof AndExpression){
                    stack.push("And");
                }
                stack.push(rhs);
                stack.push(operatorAfter);
            }
            } catch(ArrayIndexOutOfBoundsException e){
                e.printStackTrace();
            }
        BinaryCommonExpression lhs2 = (BinaryCommonExpression)popValue.getLHS();
        BinaryCommonExpression rhs = (BinaryCommonExpression)popValue.getRHS();
        stack.push(lhs2);
        if(popValue instanceof OrExpression){
            stack.push("OR");
        }else if (popValue instanceof AndExpression){
            stack.push("And");
        }
        stack.push(rhs);
    }

Here is expected result:

[EqExpression, OR, GtExpression, And, LtExpression, OR, LtExpression, OR, EqExpression]