java.util包的聚合框架应用

java.util包的集合框架应用

package mix.test;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.HashSet;
import java.util.List;
import java.util.Set;

/**
 * @function 【武汉】歪尘(531314208) 2011-10-26 20:55:54<BR>
 *           set集合有一些javabean，我要怎么进行过滤？<BR>
 *           name 数量 <BR>
 *           a 10<BR>
 *           b 3<BR>
 *           a 3<BR>
 *           b 5<BR>
 * 
 *           name 数量 <BR>
 *           a 13<BR>
 *           b 8<BR>
 * 
 * @author ocaicai@yeah.net
 * 
 * @date 2011-10-27
 */
public class ListTest {

	/**
	 * @param args
	 */
	public static void main(String[] args) {
		List<Product> list = genernateProduct();
		list = getCountByName(list);
		System.out.println(Arrays.toString(list.toArray()));
	}

	public static List<Product> genernateProduct() {
		List<Product> list = new ArrayList<Product>();
		list.add(new Product("a", 10));
		list.add(new Product("b", 3));
		list.add(new Product("a", 3));
		list.add(new Product("c", 5));
		list.add(new Product("b", 5));
		list.add(new Product("c", 7));
		return list;
	}

	public static List<Product> getCountByName(List<Product> list) {

		List<Product> targetList = new ArrayList<Product>();
		int count = 0;
		Product product = null;

		// 去除掉重复name，得到有序的name
		Set<String> nameSet = new HashSet<String>();
		List<String> nameList = new ArrayList<String>();
		for (int i = 0; i < list.size(); i++)
			nameSet.add(list.get(i).getName());
		for (String name : nameSet)
			nameList.add(name);
		Collections.sort(nameList);

		// 获取每个name的count和
		for (String name : nameList) {
			count = 0;
			for (int i = 0; i < list.size(); i++) {
				product = list.get(i);
				if (product.getName().equals(name)) {
					count += product.getCount();
					list.remove(i);
					i--;
				}
			}
			targetList.add(new Product(name, count));
		}

		return targetList;
	}
}

package mix.test;

public class Product {
	private String name;
	private int count;

	public Product(String name, int count) {
		super();
		this.name = name;
		this.count = count;
	}

	public String getName() {
		return name;
	}

	public void setName(String name) {
		this.name = name;
	}

	public int getCount() {
		return count;
	}

	public void setCount(int count) {
		this.count = count;
	}

	@Override
	public String toString() {
		return this.name + ":" + this.count;
	}
}

输出结果：

[a:13, b:8, c:12]

第二种方法，感觉思路更清晰，运算复杂度更小：getCountByName方法


	public static List<Product> getCountByName(List<Product> productList) {

		List<Product> targetList = new ArrayList<Product>();
		Product product = null;

		// 寻找该name的总count，然后删除该name
		String name = null;
		int count = 0;

		while (productList.size() > 0) {
			name = productList.get(0).getName();
			count = 0;
			for (int i = 0; i < productList.size(); i++) {
				product = productList.get(i);
				if (product.getName().equals(name)) {
					count += product.getCount();
					productList.remove(i);
					i--;
				}
			}
			targetList.add(new Product(name, count));
		}

		return targetList;
	}

java.util包的聚合框架应用

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