java Reduce的三种重载

Optional<T> reduce(BinaryOperator<T> accumulator)

T result = a[0]; 

for (int i = 1; i < n; i++) {

result = accumulator.apply(result, a[i]); 

}

return result;

T reduce(T identity, BinaryOperator<T> accumulator)

T result = identity;

for (int i = 0; i < n; i++) {

result = accumulator.apply(result, a[i]); 

}

return result;

<U> U reduce(U identity, BiFunction<U, ? super T, U> accumulator,BinaryOperator<U> combiner);

static class ScoreBean {

private String name; //学生姓名

private int score;   //分数，需要汇总该字段  

public ScoreBean(String name, int score) {

this.name = name;

this.score = score;

}

//get 和 set 方法省略

}