JDK14/Java14源码在线阅读

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 * Copyright (c) 2004, 2018, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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 */

package sun.tools.jstat;

/**
 * A class that represents a mathematical expression as a tree structure
 * containing operators as interior nodes and operands as leaves. The
 * operands can be literals or lazily bound variables.
 *
 * @author Brian Doherty
 * @since 1.5
 */
public class Expression {
    private static int nextOrdinal;
    private boolean debug = Boolean.getBoolean("Expression.debug");
    private Expression left;
    private Expression right;
    private Operator operator;
    private int ordinal = nextOrdinal++;
    private boolean required = false;

    Expression() {
        if (debug) {
            System.out.println("Expression " + ordinal + " created");
        }
    }

    void setLeft(Expression left) {
        if (debug) {
            System.out.println("Setting left on " + ordinal + " to " + left);
        }
        this.left = left;
        this.left.setRequired(required);
    }

    Expression getLeft() {
        return left;
    }

    void setRight(Expression right) {
        if (debug) {
            System.out.println("Setting right on " + ordinal + " to " + right);
        }
        this.right = right;
        this.right.setRequired(required);
    }

    Expression getRight() {
        return right;
    }

    void setOperator(Operator o) {
        if (debug) {
            System.out.println("Setting operator on " + ordinal + " to " + o);
        }
        this.operator = o;
    }

    Operator getOperator() {
        return operator;
    }

    void setRequired(boolean r) {
        this.required = r;
        if (left != null) {
            left.setRequired(required);
        }
        if (right != null) {
            right.setRequired(required);
        }
    }

    boolean isRequired() {
        return required;
    }

    public String toString() {

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