Java 向表达式树添加括号

我试图编写一个函数，给定一棵树，创建一个中缀表达式，只需要括号。例如，如果表达式（（a-3）-（b-5））已输入到树中，则此函数将返回字符串a-3-（b-5）或（（a-3）（b-5））返回（a-3）（b-5）[出于某种原因，它不会在这些表达式之间显示*]。我现在有一个函数，它将整个表达式括在括号中，这是它返回的第一个示例（a-3-b-5）。有人能解释一下是什么导致它a）没有在每个表达式中添加括号，b）如何修改它以只添加所需的括号

编辑：稍微修改，使每个表达式现在都有括号，而不是整个表达式。现在产生（a-3）-（b-5）作为输出

private String inorder(ExpTree t) {
    if (t != null) {
        //if node and left child are operators
        if (t.type == 2) {
            if (getPri(t) <= getPri(parent) && t != parent) {
                strBuf.append('(');
            }
        }
        inorder(t.lChild, t);
        strBuf.append(t.leafVal);
        inorder(t.rChild, t);
        //if node and right child are operators
        if (t.type == 2) {
            if (getPri(t) <= getPri(parent) && t != parent) {
                strBuf.append(')');
            }
        }
    }
    return strBuf.toString();

private int getPri(ExpTree t) {
    String leaf = "";
    if (t.type == 2) {
        leaf = t.leafVal.toString();
    }
    else {
        return 0;
    }
    if (leaf == "*" || leaf == "%" || leaf == "/") {
        return 2;
    }
    else if (leaf == "+" || leaf == "-") {
        return 1;
    }
    return 0;
}

public class ExpTree {
private int type;
private Object leafVal;
private ExpTree lChild, rChild;
public static final int NUM = 0, VAL = 1, OP = 2;

public ExpTree(int type, Object leafVal, ExpTree l, ExpTree r) {
    this.type = type;
    this.leafVal = leafVal;
    this.lChild = l;
    this.rChild = r;
}