### Question:
ColumnCombination implements Serializable, Comparable<Object> { @Override public int compareTo(Object o) { if (o != null && o instanceof ColumnCombination) { ColumnCombination other = (ColumnCombination) o; int lengthComparison = this.columnIdentifiers.size() - other.columnIdentifiers.size(); if (lengthComparison != 0) { return lengthComparison; } else { Iterator<ColumnIdentifier> otherIterator = other.columnIdentifiers.iterator(); int equalCount = 0; int negativeCount = 0; int positiveCount = 0; while (otherIterator.hasNext()) { ColumnIdentifier currentOther = otherIterator.next(); for (ColumnIdentifier currentThis : this.columnIdentifiers) { int currentComparison = currentThis.compareTo(currentOther); if (currentComparison == 0) { equalCount++; } else if (currentComparison > 0) { positiveCount++; } else if (currentComparison < 0) { negativeCount++; } } } if (equalCount == this.columnIdentifiers.size()) { return 0; } else if (positiveCount > negativeCount) { return 1; } else { return -1; } } } else { return 1; } } ColumnCombination();  ColumnCombination(ColumnIdentifier... columnIdentifier); Set<ColumnIdentifier> getColumnIdentifiers(); void setColumnIdentifiers(Set<ColumnIdentifier> identifiers); @Override String toString(); String toString(Map<String, String> tableMapping, Map<String, String> columnMapping); static ColumnCombination fromString(Map<String, String> tableMapping, Map<String, String> columnMapping, String str); @Override int hashCode(); @Override int compareTo(Object o); @Override boolean equals(Object obj); static final String COLUMN_CONNECTOR; }### Answer:
@Test public void testCompareTo() { ColumnIdentifier column11 = new ColumnIdentifier("table1", "column1"); ColumnIdentifier column12 = new ColumnIdentifier("table2", "column2"); ColumnIdentifier column13 = new ColumnIdentifier("table3", "column4"); ColumnCombination columnCombination1 = new ColumnCombination(column12, column13, column11); ColumnIdentifier column21 = new ColumnIdentifier("table1", "column1"); ColumnIdentifier column22 = new ColumnIdentifier("table2", "column2"); ColumnIdentifier column23 = new ColumnIdentifier("table3", "column2"); ColumnCombination columnCombination2 = new ColumnCombination(column21, column22, column23); assertTrue(columnCombination1.compareTo(columnCombination2) > 0); assertTrue(columnCombination1.compareTo(columnCombination1) == 0); assertTrue(columnCombination2.compareTo(columnCombination2) == 0); assertTrue(columnCombination2.compareTo(columnCombination1) < 0); }