项目中有需要多次统计 某些集合中 的某个属性值，所以考虑封装一个方法，让其其定义实现计算方式。 话不多说，看代码：
1、封装的自定义集合工具类：CollectionsCustom
package com.test.util;
import java.util.Collection;
import org.apache.commons.collections.CollectionUtils;
public class CollectionsCustom {
public static Output reduce(Collection original, Output initValue, ReduceFunction reduceFunction) {
Output result = initValue;
if (CollectionUtils.isEmpty(original)) {
return result;
}
if (reduceFunction == null) {
return result;
}
for (Input input : original) {
result = reduceFunction.apply(input, result);
}
return result;
}
public interface ReduceFunction {
Result apply(Input input, Result lastResult);
}
}
2、测试类TestCollections
package com.test;
import java.math.BigDecimal;
import java.util.Arrays;
import java.util.List;
import com.test.util.CollectionsCustom;
public class TestCollection {
private static List list = Arrays.asList(
new User("张三", BigDecimal.valueOf(35.6), 18),
new User("李四", BigDecimal.valueOf(85), 30),
new User("赵六", BigDecimal.valueOf(66.55), 25));
public static void main(String[] args) {
//统计集合内分数之和
testTotalScore();
//统计集合内年龄之和
testTotalAge();
}
private static void testTotalScore(){
//统计集合内分数之和
BigDecimal totalScore = CollectionsCustom.reduce(list, BigDecimal.ZERO, new CollectionsCustom.ReduceFunction() {
@Override
public BigDecimal apply(User input, BigDecimal lastResult) {
// TODO Auto-generated method stub
return lastResult.add(input.getScore());
}
});
System.out.println("总共分数：" + totalScore);
}
private static void testTotalAge(){
//统计集合内年龄之和
Integer totalAge = CollectionsCustom.reduce(list, 0, new CollectionsCustom.ReduceFunction() {
@Override
public Integer apply(User input, Integer lastResult) {
// TODO Auto-generated method stub
return lastResult += input.getAge();
}
});
System.out.println("总共年龄：" + totalAge);
}
static class User{
private String userName; //姓名
private BigDecimal score;//分数
private Integer age;
public String getUserName() {
return userName;
}
public void setUserName(String userName) {
this.userName = userName;
}
public BigDecimal getScore() {
return score;
}
public void setScore(BigDecimal score) {
this.score = score;
}
public Integer getAge() {
return age;
}
public void setAge(Integer age) {
this.age = age;
}
public User(String userName, BigDecimal score, Integer age) {
super();
this.userName = userName;
this.score = score;
this.age = age;
}
public User() {
// TODO Auto-generated constructor stub
}
}
}
3、测试输出结果：
总共分数：187.15
总共年龄：73
这里如果传入的是封装类型Integer等，最好自己做下非空处理。相信高质量的封装代码能为你自己加分的！
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