Java 通过stream()获取找到List(列表)中最小的对象元素

class Foo {    private int variableCount;    public Foo(int vars) {        this.variableCount = vars;     }    public Integer getVariableCount() {       return variableCount;     }}

1、实现accumulator object用于给Collector提供函数

/**
 * Accumulator object to hold the current min
 * and the list of Foos that are the min.
 */
class Accumulator {
    Integer min;
    List foos;
    Accumulator() {
        min = Integer.MAX_VALUE;
        foos = new ArrayList<>();
    }
    void accumulate(Foo f) {
        if (f.getVariableCount() != null) {
            if (f.getVariableCount() < min) {
                min = f.getVariableCount();
                foos.clear();
                foos.add(f);
            } else if (f.getVariableCount() == min) {
                foos.add(f);
            }
        }
    }
    Accumulator combine(Accumulator other) {
        if (min < other.min) {
            return this;
        }
        else if (min > other.min) {
            return other;
        }
        else {
            foos.addAll(other.foos);
            return this;
        }
    }
    List getFoos() { return foos; }
}

2、调用方法和测试

1）示例List

List foos = Arrays.asList(new Foo(3), new Foo(3), new Foo(2), new Foo(1), new Foo(1), new Foo(4));

2）调用方法

List mins = foos.stream().collect(Collector.of(    Accumulator::new,    Accumulator::accumulate,    Accumulator::combine,    Accumulator::getFoos    ));

输出结果：

[Foo{1}, Foo{1}]