### Question:
AbstractVector implements Vector, LengthCachingVector { @Override public double getDistanceSquared(Vector v) { if (size != v.size()) { throw new CardinalityException(size, v.size()); } double d1; double d2; double dot; if (lengthSquared >= 0) { d1 = lengthSquared; d2 = v.getLengthSquared(); dot = this.dot(v); } else { d1 = 0; d2 = v.getLengthSquared(); dot = 0; final Iterator<Element> i = iterateNonZero(); while (i.hasNext()) { Element e = i.next(); double value = e.get(); d1 += value * value; dot += value * v.getQuick(e.index()); } lengthSquared = d1; } double r = d1 + d2 - 2 * dot; if (r > 1.0e-3 * (d1 + d2)) { return Math.max(0, r); } else { if (this.isSequentialAccess()) { if (v.isSequentialAccess()) { return mergeDiff(this, v); } else { return randomScanDiff(this, v); } } else { return randomScanDiff(v, this); } } } protected  AbstractVector(int size); @Override double aggregate(DoubleDoubleFunction aggregator, DoubleFunction map); @Override double aggregate(Vector other, DoubleDoubleFunction aggregator, DoubleDoubleFunction combiner); @Override Vector viewPart(int offset, int length); @Override Vector clone(); @Override Vector divide(double x); @Override double dot(Vector x); @Override double get(int index); @Override Element getElement(int index); @Override Vector normalize(); @Override Vector normalize(double power); @Override Vector logNormalize(); @Override Vector logNormalize(double power); Vector logNormalize(double power, double normLength); @Override double norm(double power); @Override double getLengthSquared(); @Override void invalidateCachedLength(); @Override double getDistanceSquared(Vector v); @Override double maxValue(); @Override int maxValueIndex(); @Override double minValue(); @Override int minValueIndex(); @Override Vector plus(double x); @Override Vector plus(Vector x); @Override Vector minus(Vector that); @Override void set(int index, double value); @Override void incrementQuick(int index, double increment); @Override Vector times(double x); @Override Vector times(Vector x); @Override double zSum(); @Override int getNumNonZeroElements(); @Override Vector assign(double value); @Override Vector assign(double[] values); @Override Vector assign(Vector other); @Override Vector assign(DoubleDoubleFunction f, double y); @Override Vector assign(DoubleFunction function); @Override Vector assign(Vector other, DoubleDoubleFunction function); @Override Matrix cross(Vector other); @Override final int size(); @Override String asFormatString(); @Override int hashCode(); @Override boolean equals(Object o); @Override String toString(); String toString(String[] dictionary);  }### Answer:
@Test public void testGetDistanceSquared() { Vector other = new RandomAccessSparseVector(test.size()); other.set(1, -2); other.set(2, -5); other.set(3, -9); other.set(4, 1); double expected = test.minus(other).getLengthSquared(); assertTrue("a.getDistanceSquared(b) != a.minus(b).getLengthSquared", Math.abs(expected - test.getDistanceSquared(other)) < 10.0E-7); }