Artist:

package com.pptb.java8.learning;

import java.util.List;

public class Artist {
    public String name;
    public List<String> members;
    public String origin;
}

Track:

package com.pptb.java8.learning;

public class Track {
    public String name;
}

Album:

package com.pptb.java8.learning;

import java.util.List;

public class Album {
    public String name;
    public List<Track> tracks;
    public List<String> musicians;
}