函數式編程 Closure 閉包 封裝特定的業務功能

剛接觸Java的編程基本都是面向對象的編程思維，偶爾遇到複雜的算法，也是採取基本的容器+變量組合形式。org.apache.commons.collections4.Closure類的閉包操作，可以自定義需要的處理邏輯，對於多的數據操作，簡化了編程的力度，也提高了代碼的可讀性。

import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
import org.apache.commons.collections4.Closure;
import org.apache.commons.collections4.CollectionUtils;
import org.apache.commons.collections4.Predicate;
import org.apache.commons.collections4.functors.ChainedClosure;
import org.apache.commons.collections4.functors.IfClosure;
import org.apache.commons.collections4.functors.WhileClosure;

/**
 函數式編程 Closure 閉包 封裝特定的業務功能
 1、Closure
 2、IfClosure  IfClosure.ifClosure(斷言,功能1,功能2)
 3、WhileClosure WhileClosure.whileClosure(斷言,功能,標識) 
 4、ChainedClosure.chainedClosure(功能列表);
 CollectionUtils.forAllDo(容器,功能類對象);
 */
public class ClosureDemo {
	/**
	 * 基本操作
	 */
	public static void basic(){
		List<Employee> empList = new ArrayList<Employee>();
		empList.add(new Employee("xxjsb",20000));
		empList.add(new Employee("is",10000));
		empList.add(new Employee("good",5000));
		//業務功能
		Closure<Employee> cols = new Closure<Employee>(){
			public void execute(Employee emp) {
				emp.setSalary(emp.getSalary()*1.2);
			}};
		//工具類
		CollectionUtils.forAllDo(empList,cols)	;
		//操作後的數據
		Iterator<Employee> empIt = empList.iterator();
		while(empIt.hasNext()){
			System.out.println(empIt.next());
		}
		//xxjsb:24000.0,is:12000.0,good:6000.0
	}
	/**
	 * 二選一  如果是打折商品,8折處理;否則滿90減20
	 */
	public static void ifClosure(){
		List<Goods> goodsList = new ArrayList<Goods>();
		goodsList.add(new Goods("JAVASE",120,true));
		goodsList.add(new Goods("JAVAEE",100,false));
		goodsList.add(new Goods("數據庫",80,false));
		//滿90減20
		Closure<Goods> subtract = new Closure<Goods>(){
			public void execute(Goods goods) {
				if(goods.getPrice()>=90){
					goods.setPrice(goods.getPrice()-20);
				}
			}};
		//8折
		Closure<Goods> discount = new Closure<Goods>(){
			public void execute(Goods goods) {
				if(goods.isDiscount()){
					goods.setPrice(goods.getPrice()*0.8);
				}
			}};	
		//判斷是否打折商品
		Predicate<Goods> pre = new Predicate<Goods>(){
			public boolean evaluate(Goods goods) {
				return goods.isDiscount();
			}}; 
		//二選一:先判斷是否打折?是:8折處理;否:滿90減20
		Closure<Goods> ifClo = IfClosure.ifClosure(pre,discount,subtract);
		CollectionUtils.forAllDo(goodsList,ifClo);
		for(Goods temp:goodsList){
			System.out.println(temp);
		}
		//JAVASE:96.0,打折;JAVAEE:80.0,不打折;數據庫:80.0,不打折
	}
	/**
	 * 確保所有的員工工資都大於10000,如果已經超過的不再上漲
	 */
	public static void whileClosure(){
		List<Employee> empList = new ArrayList<Employee>();
		empList.add(new Employee("xxjsb",20000));
		empList.add(new Employee("is",10000));
		empList.add(new Employee("good",5000));
		//業務功能 每次上漲0.2 
		Closure<Employee> cols = new Closure<Employee>(){
			public void execute(Employee emp) {
				emp.setSalary(emp.getSalary()*1.2);
			}};
		//判斷:工資是否大於10000
		Predicate<Employee> empPre = new Predicate<Employee>(){
			@Override
			public boolean evaluate(Employee emp) {
				return emp.getSalary()<10000;
			}			
		};	
		//false:while結構 先判斷後執行;true:do..while 先執行後判斷
		Closure<Employee> whileCols = WhileClosure.whileClosure(empPre,cols,false);
		CollectionUtils.forAllDo(empList,whileCols)	;
		Iterator<Employee> empIt = empList.iterator();
		while(empIt.hasNext()){
			System.out.println(empIt.next());
		}
		//xxjsb:20000.0,is:10000.0,good:10368.0
	}
	/**
	 * 折上減   先打折商品,進行8折,滿90再減10
	 */
	@SuppressWarnings("unchecked")
	public static void chainClosure(){
		List<Goods> goodsList =new ArrayList<Goods>();
		goodsList.add(new Goods("JAVASE",120,true));
		goodsList.add(new Goods("JAVAEE",100,false));
		goodsList.add(new Goods("數據庫",80,false));
		//滿90減10
		Closure<Goods> subtract = new Closure<Goods>(){
			public void execute(Goods goods) {
				if(goods.getPrice()>=90){
					goods.setPrice(goods.getPrice()-10);
				}
			}};
		//打折
		Closure<Goods> discount = new Closure<Goods>(){
			public void execute(Goods goods) {
				if(goods.isDiscount()){
					goods.setPrice(goods.getPrice()*0.8);
				}
			}};	
		//鏈式操作
		Closure<Goods> chainClo = ChainedClosure.chainedClosure(discount,subtract);
		CollectionUtils.forAllDo(goodsList,chainClo);
		for(Goods temp:goodsList){
			System.out.println(temp);
		}
		//JAVASE:86.0,打折;JAVAEE:90.0,不打折;數據庫:80.0,不打折
	}
}
class Goods {
	private String name;
	private double price;
	private boolean discount;//折扣
	public Goods() {
	}
	public Goods(String name, double price, boolean discount) {
		super();
		this.name = name;
		this.price = price;
		this.discount = discount;
	}
	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 boolean isDiscount() {
		return discount;
	}
	public void setDiscount(boolean discount) {
		this.discount = discount;
	}
	@Override
	public String toString() {
		return this.name+":"+this.price+","+(discount?"打折":"不打折");
	}
}

class Employee {
	private String name;
	private double salary;
	//alt +/
	public Employee() {
	}
	//alt+shift+s  o
	public Employee(String name, double salary) {
		super();
		this.name = name;
		this.salary = salary;
	}
	//alt+shift+s  +r tab 回車 shift+tab 回車
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	public double getSalary() {
		return salary;
	}
	public void setSalary(double salary) {
		this.salary = salary;
	}
	@Override
	public String toString() {
		return this.name+":"+this.salary;
	}
}