  By using a test-function method, we construct $n$ exact solutions of a
quantum harmonic oscillator with a time-dependent "spring constant". Any $n$-th
solution describes a wave-packet train consisting of $n+1$ packets. Its center
oscillates like the classically harmonic oscillator with variable frequency,
and width and highness of each packet change simultaneously. When the
deformation is small, it behaves like a soliton train, and the large
deformation is identified with collapse and revival of the wave-packet train.
