ElementComparator.java

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 * Copyright (C) 1997-2007  The Chemistry Development Kit (CDK) project
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package org.openscience.cdk.tools;

import org.openscience.cdk.annotations.TestClass;
import org.openscience.cdk.annotations.TestMethod;

import java.util.Comparator;

/** 
  * Compares elements based on the order commonly used in 
  * molecular formula. Order:
  * C, H, other elements in alphabetic order.
  *
  * @cdk.module standard
 * @cdk.githash
  *
  * @cdk.keyword element, sorting
  */
@TestClass("org.openscience.cdk.tools.ElementComparatorTest")
public class ElementComparator implements Comparator {

    private static final String H_ELEMENT_SYMBOL = "H";
    private static final String C_ELEMENT_SYMBOL = "C";
    
    /**
     * Returns a negative if o1 comes before o2 in a molecular formula,
     * returns zero if they are identical, and positive if o1 comes
     * after o2 in the formula.
     */
    @TestMethod("testCompare_Object_Object")
    public int compare(Object o1, Object o2) {
        if (C_ELEMENT_SYMBOL.equals(o1)) {
            if (C_ELEMENT_SYMBOL.equals(o2)) {
                return 0;
            } else {
                return -1;
            }
        } else if (H_ELEMENT_SYMBOL.equals(o1)) {
            if (C_ELEMENT_SYMBOL.equals(o2)) {
                return 1;
            } else if (H_ELEMENT_SYMBOL.equals(o2)) {
                return 0;
            } else {
                return -1;
            }
        } else {
            if (C_ELEMENT_SYMBOL.equals(o2) || H_ELEMENT_SYMBOL.equals(o2)) {
                return 1;
            } else {
                return ((String)o1).compareTo((String)o2);
            }
        }
    }

}