接口节点和ExpressionTree

Question

所以我试着建立这个树。我有我的界面Node，现在我正在尝试将节点添加到树中。这是我到目前为止所拥有的。每次我遍历我的字符串并找到一个数字我想把它放入一个节点，然后将该节点添加到我的树。但每次我尝试这是我得到一个错误。请帮忙。

import java.util.ArrayList;
import java.util.Stack;
import javax.swing.tree.TreeNode;
import java.lang.*;

public class BinaryExpressionTree  {    

    boolean isOperator(String c) {
        if (c == "+" || c == "-" || c == "*" || c == "/") {
            return true;
        }
        return false;
    }


    @SuppressWarnings({ "unchecked", "rawtypes" })
    public void  constructTree(String postfix[]) {
        Stack<Node> stackTree = new Stack<>();

        Node<String> n1;
        Node n2;
        Node n3;

        for(int i = 0; i <= postfix.length; i++){
            if(!isOperator(postfix[i])) {
                n1 = postfix[i];
            }


            }else {

            }

        }

    }

以下是我的Node界面的外观： 我还创建了实现它的OperandNode和OperatorNode。

public interface Node<T> {

    public T GetData() ;

    public void SetLeft(Node Node);

    public Node GetLeft();

    public void SetRight(Node Node);

    public Node GetRight();


}

OperandNode类

public class OperandNode implements Node<Integer> {

    int operandData;
    Node leftNode;
    Node rightNode;

    private OperandNode(int operandData, Node leftNode, Node rightNode){
        this.operandData = operandData;
        this.leftNode = leftNode;
        this.rightNode = rightNode;
    }

    public Integer GetData() {      
        return operandData;
    }

    public void SetLeft(Node leftNode) {
        this.leftNode = leftNode;
    }

    public Node GetLeft() {
        return leftNode;
    }

    public void SetRight(Node rightNode) {
        this.rightNode = rightNode;
    }

    public Node GetRight() {
        return rightNode;
    }

}