SparseVector extends Vector { @Override public SparseVector append(double d) { int[] indices = new int[this.indices.length + 1]; double[] values = new double[this.values.length + 1]; int n = (this.n >= 0) ? this.n + 1 : this.n; System.arraycopy(this.indices, 0, indices, 0, this.indices.length); System.arraycopy(this.values, 0, values, 0, this.values.length); indices[this.indices.length] = n - 1; values[this.values.length] = d; return new SparseVector(n, indices, values); } SparseVector();  SparseVector(int n);  SparseVector(int n, int[] indices, double[] values);  SparseVector(int n, Map<Integer, Double> kv); @Override SparseVector clone(); @Override SparseVector prefix(double d); @Override SparseVector append(double d); int[] getIndices(); double[] getValues(); @Override int size(); @Override double get(int i); void setSize(int n); int numberOfValues(); @Override void set(int i, double val); @Override void add(int i, double val); @Override String toString(); @Override double normL2(); @Override double normL1(); @Override double normInf(); @Override double normL2Square(); @Override SparseVector slice(int[] indices); @Override Vector plus(Vector vec); @Override Vector minus(Vector vec); @Override SparseVector scale(double d); @Override void scaleEqual(double d); void removeZeroValues(); @Override double dot(Vector other); @Override DenseMatrix outer(); DenseMatrix outer(SparseVector other); DenseVector toDenseVector(); @Override void standardizeEqual(double mean, double stdvar); @Override void normalizeEqual(double p); @Override boolean equals(Object o); @Override int hashCode(); void forEach(BiConsumer<Integer, Double> action); @Override VectorIterator iterator();  }
@Test public void testAppend() throws Exception { SparseVector prefixed = v1.append(0.2); Assert.assertArrayEquals(prefixed.getIndices(), new int[]{1, 3, 5, 7, 8}); Assert.assertArrayEquals(prefixed.getValues(), new double[]{2, 2, 2, 2, 0.2}, 0); }