Java8 ラムダ式でComparatorのコールバック関数を簡単に書く方法 ref: https://qiita.com/shisama/items/1ba7e4f0000d4e7a9b5e

Java7.java

Collections.sort(list, new Comparator<Person>(){
    @Override
    public int compare(Person p1, Person p2) {
        int ret = p1.getId() - p2.getId();
        if (ret == 0) {
            ret = p1.getName().compareTo(p2.getName());
        }
        if (ret == 0) {
            ret = p1.getAge() - p2.getAge();
        }
        return ret;
    }       
});

Java8.java

Collections.sort(list, (p1, p2) -> {
    int ret = Integer.compare(p1.getId(), p2.getId());
    if (ret == 0) {
        ret = p1.getName().compareTo(p2.getName();
    }    
    if (ret == 0) {
        ret = Integer.compare(p1.getAge(), p2.getAge());
    }
    return ret;
});