lambdaj学习

原文地址：http://www.thinksaas.cn/topics/0/83/83436.html

package info.yiwen.data;

/**
 * 测试用bean对象，产品
 * @author 乔学士
*
*/
public class Product {

private int id;
private String name;
private double price;
private double weight;
private String type;

public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public double getPrice() {
return price;
}
public void setPrice(double price) {
this.price = price;
}
public double getWeight() {
return weight;
}
public void setWeight(double weight) {
this.weight = weight;
}
public String getType() {
return type;
}
public void setType(String type) {
this.type = type;
}
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
@Override
public String toString() {
return"Product [id="+ id +", name="+ name +", price="+ price
+", type="+ type +", weight="+ weight +"]";
}
}

package info.yiwen.data;

import java.util.ArrayList;
import java.util.List;
import java.util.Random;


/**
 * 生产产品的工厂
 * @author 乔学士
*
*/
public class ProductFactory {

public static List<Product> genRandomProduct(int amount){
if(amount < 0 ){
amount = 1;
}
Random random = new Random();
List<Product> ps = new ArrayList<Product>(amount);
for(int i = 0; i < amount; i++){
Product p = new Product();
int randomNum = random.nextInt(100); 
p.setId(i+1);
p.setId(i+1);
p.setName("name"+ randomNum);
p.setPrice(Math.round(random.nextDouble() * 1000));
p.setWeight(Math.round(random.nextDouble() * 1000));
p.setType("type"+ randomNum);
ps.add(p);
}

return ps;
}
}

package info.yiwen.test;
import java.util.Iterator;
import java.util.List;
import java.util.Map;

import ch.lambdaj.function.closure.Closure;


import info.yiwen.data.Product;
import info.yiwen.data.ProductFactory;
import static ch.lambdaj.Lambda.*;
import static ch.lambdaj.collection.LambdaCollections.*;
import static org.hamcrest.Matchers.*;

/**
 * 测试类，方便起见，没有用jUnit
 * @author 乔学士
*
*/
public class Test {
public static void main(String[] args) {
List<Product> ps = ProductFactory.genRandomProduct(10);

printl(1);
//1.简单例子
//对每个product都设置price为100
//forEach(ps).setPrice(100); //对每个product都设置setPrice为100
//按重量从小到大进行排序
ps = sort(ps, on(Product.class).getWeight()); 
print(ps);

printl(2);
//2.joinFrom 连接某个属性,中间默认用逗号加空格(","), 可以自定义分隔符
//连接每个product对象的name
String names = joinFrom(ps).getName();
//连接每个product对象的name，间隔符为":"
String names2 = joinFrom(ps,":").getName();
System.out.println(names);
System.out.println(names2);

printl(3);
//3.select
//从ps中选择出重量大于等于500的
List<Product> ps2 = select(ps,
//注意下面greaterThanOrEqualTo方法中参数的类型一定要和getWeight严格相等
having(on(Product.class).getWeight(), greaterThanOrEqualTo(new Double(500)))
);
System.out.println(ps2);

printl(4);
//4.selectMin找到最小的, also selectMax
//找到重量最轻的产品
Product p = selectMin(ps, on(Product.class).getWeight());
System.out.println(p);

printl(5);
//5.max and maxFrom, also min and minFrom
//找到最重的产品的重量（两种方法）
//5.1
double weight1 = max(ps, on(Product.class).getWeight());
//5.2
double weight2 = maxFrom(ps).getWeight();
System.out.println(weight1 +","+ weight2);

printl(6);
//6.extract,抽取所有对象的某一列返回值
//得到每个产品的id
//6.1 使用on
List<Integer> ids = extract(ps, on(Product.class).getId());
System.out.println(ids);
//6.2 使用属性名
List<?> ids2 = extractProperty(ps,"id");
System.out.println(ids2);

printl(7);
//7.index 返回一个map，value是每个对象，key是对象的某个属性
//返回一个key为id，value是对象的Map
Map<Integer, ?> map = index(ps, on(Product.class).getId()); 
print(map);


printl(8);
//8.with 使用更为流畅的方法
//找到重量大于400的产品的id列表，并排序

//8.1原始方法
List<Double> prices1 = sort(
extract(
select(ps, having(on(Product.class).getWeight(), greaterThan(400.0))),
on(Product.class).getPrice()
),
on(Double.class).doubleValue()
);

//8.2使用with的方法
List<Double> prices2 = with(ps)
.retain(having(on(Product.class).getWeight(), greaterThan(400.0)))
.extract(on(Product.class).getPrice())
.sort(on(Double.class).doubleValue());

System.out.println(prices1);
System.out.println(prices2);

printl(9);
//9.闭包 ，of(T t) 返回T类型
Closure println = closure(); //创建一个closure，放到ThreadLocal中
of(System.out).println(var(String.class)); //of方法从ThreadLocal中得到这个Closure
println.apply("hello");
println.each("hello","oschina");
}

static void print(Iterable<?> ps){
Iterator<?> it = ps.iterator();
while(it.hasNext()){
System.out.println(it.next());
}
}
static void print(Map<?, ?> map){
for(Map.Entry<?, ?> e :map.entrySet()){
System.out.println(e.getKey() +":"+ e.getValue());
}
}

static void printl(int itemNo){
System.out.println("--------------------"+ itemNo +"---------------------");
}
}

--------------------1---------------------
Product [id=4, name=name22, price=56.0, type=type22, weight=193.0]
Product [id=6, name=name24, price=35.0, type=type24, weight=194.0]
Product [id=9, name=name48, price=371.0, type=type48, weight=417.0]
Product [id=8, name=name95, price=981.0, type=type95, weight=434.0]
Product [id=5, name=name22, price=566.0, type=type22, weight=594.0]
Product [id=2, name=name83, price=249.0, type=type83, weight=764.0]
Product [id=10, name=name17, price=359.0, type=type17, weight=855.0]
Product [id=7, name=name30, price=203.0, type=type30, weight=877.0]
Product [id=3, name=name94, price=897.0, type=type94, weight=981.0]
Product [id=1, name=name55, price=714.0, type=type55, weight=991.0]
--------------------2---------------------
name22, name24, name48, name95, name22, name83, name17, name30, name94, name55
name22:name24:name48:name95:name22:name83:name17:name30:name94:name55
--------------------3---------------------
[Product [id=5, name=name22, price=566.0, type=type22, weight=594.0], Product [id=2, name=name83, price=249.0, type=type83, weight=764.0], Product [id=10, name=name17, price=359.0, type=type17, weight=855.0], Product [id=7, name=name30, price=203.0, type=type30, weight=877.0], Product [id=3, name=name94, price=897.0, type=type94, weight=981.0], Product [id=1, name=name55, price=714.0, type=type55, weight=991.0]]
--------------------4---------------------
Product [id=4, name=name22, price=56.0, type=type22, weight=193.0]
--------------------5---------------------
991.0,991.0
--------------------6---------------------
[4, 6, 9, 8, 5, 2, 10, 7, 3, 1]
[4, 6, 9, 8, 5, 2, 10, 7, 3, 1]
--------------------7---------------------
1:Product [id=1, name=name55, price=714.0, type=type55, weight=991.0]
2:Product [id=2, name=name83, price=249.0, type=type83, weight=764.0]
3:Product [id=3, name=name94, price=897.0, type=type94, weight=981.0]
4:Product [id=4, name=name22, price=56.0, type=type22, weight=193.0]
5:Product [id=5, name=name22, price=566.0, type=type22, weight=594.0]
6:Product [id=6, name=name24, price=35.0, type=type24, weight=194.0]
7:Product [id=7, name=name30, price=203.0, type=type30, weight=877.0]
8:Product [id=8, name=name95, price=981.0, type=type95, weight=434.0]
9:Product [id=9, name=name48, price=371.0, type=type48, weight=417.0]
10:Product [id=10, name=name17, price=359.0, type=type17, weight=855.0]
--------------------8---------------------
[203.0, 249.0, 359.0, 371.0, 566.0, 714.0, 897.0, 981.0]
[203.0, 249.0, 359.0, 371.0, 566.0, 714.0, 897.0, 981.0]
--------------------9---------------------
hello
hello
oschina