问题
之前写了一个小的燃烧计算程序，其中有一部分是为了计算混合组分的特性参数，用了下面的一些代码。
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| public interface ComponentCal extends Map<String, Double> {
public double getDensity();
public double getQd();
public double getQg();
public double getL_O2();
public double getCp(double temperature);
public double getC();
public double getH();
}
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其中各get方法是读取各成分各自的特性参数，然后计算成混合组分的参数。
方法一
最开始写的时候用最苯的方法，用是for-each方法读取每个，然后sum方法求和。
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| public class GasComponent extends HashMap<String, Double> implements ComponentCal {
private PropertyRepository propertyRepository;
@Inject
public void setPropertyRepository(PropertyRepository propertyRepository) {
this.propertyRepository = propertyRepository;
}
public double getDensity() {
double sum = 0.0;
for (Entry<String, Double> item : this.entrySet()) {
sum += propertyRepository.getByName(item.getKey()).getDensity() * item.getValue();
}
return sum * 0.01;
}
public double getQd() {
double sum = 0.0;
for (Entry<String, Double> item : this.entrySet()) {
sum += propertyRepository.getByName(item.getKey()).getQd() * item.getValue();
}
return sum;
}
}
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方法二
用lambda取代for-each，这个感觉和C#的LINQ很像哦。
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| public class GasComponent extends HashMap<String, Double> implements ComponentCal {
private PropertyRepository propertyRepository;
@Inject
public void setPropertyRepository(PropertyRepository propertyRepository) {
this.propertyRepository = propertyRepository;
}
public double getDensity() {
return this.entrySet().stream().mapToDouble(item -> propertyRepository.getByName(item.getKey()).getDensity() * item.getValue()).sum() * 0.01;
}
public double getQd() {
return this.entrySet().stream().mapToDouble(item -> propertyRepository.getByName(item.getKey()).getQd() * item.getValue()).sum();
}
}
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方法三
上面GasComponent实现ComponentCal各个get方法时，只是有一点点不同，于是想应该可以把其简化，最开始想到的就是用反射，方法名用String来代替，调用的时候传递一个String就行了。
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| public class GasComponent extends HashMap<String, Double> implements ComponentCal {
private PropertyRepository propertyRepository;
@Inject
public void setPropertyRepository(PropertyRepository propertyRepository) {
this.propertyRepository = propertyRepository;
}
private double getPropertySum(String methodName, double factor) throws NoSuchMethodException, SecurityException {
Method method;
method = Property.class.getMethod(methodName);
return this.entrySet().stream().mapToDouble(item -> {
try {
return Double.parseDouble(method.invoke(propertyRepository.getByName(item.getKey())).toString()) * item.getValue();
} catch (NumberFormatException e) {
e.printStackTrace();
} catch (IllegalAccessException e) {
e.printStackTrace();
} catch (IllegalArgumentException e) {
e.printStackTrace();
} catch (InvocationTargetException e) {
e.printStackTrace();
}
return 0.0;
}).sum() * factor;
}
public double getDensity() {
double sum = 0.0;
try {
sum = getPropertySum("getDensity", 0.01);
} catch (NoSuchMethodException e) {
e.printStackTrace();
} catch (SecurityException e) {
e.printStackTrace();
}
return sum;
}
public double getQd() {
double sum = 0.0;
try {
sum = getPropertySum("getQd", 1.0);
} catch (NoSuchMethodException e) {
e.printStackTrace();
} catch (SecurityException e) {
e.printStackTrace();
}
return sum;
}
}
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方法四
我去，看着反射方法里面的各种try-catch好烦啊，正好前段时间在学习Java8 In Action，于是想到了函数式编程里讲到的东东。试试吧。
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| public class GasComponent extends HashMap<String, Double> implements ComponentCal {
private PropertyRepository propertyRepository;
@Inject
public void setPropertyRepository(PropertyRepository propertyRepository) {
this.propertyRepository = propertyRepository;
}
@FunctionalInterface
private interface Functional {
double getProperty(Property property);
}
private Functional fDensity = p->p.getDensity();
private Functional fQd = p->p.getQd();
private Functional fQg = p->p.getQg();
private Functional fL_O2 = p->p.getL_O2();
private Functional fC = p->p.getC();
private Functional fH = p->p.getH();
private double getPropertySum(Functional f, double factor) {
return this.entrySet().stream().mapToDouble(item -> f.getProperty(propertyRepository.getByName(item.getKey())) * item.getValue()).sum() * factor;
}
public double getDensity() {
return getPropertySum(fDensity, 0.01);
}
public double getQd() {
return getPropertySum(fQd, 1.0);
}
}
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哈哈哈，各种清爽啊。发现其实可以直接把labmda表达式用参数形式传过去嘛。
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| public class GasComponent extends HashMap<String, Double> implements ComponentCal {
private PropertyRepository propertyRepository;
@Inject
public void setPropertyRepository(PropertyRepository propertyRepository) {
this.propertyRepository = propertyRepository;
}
@FunctionalInterface
private interface Functional {
double getProperty(Property property);
}
private double getPropertySum(Functional f, double factor) {
return this.entrySet().stream().mapToDouble(item -> f.getProperty(propertyRepository.getByName(item.getKey())) * item.getValue()).sum() * factor;
}
public double getDensity() {
return getPropertySum(p -> p.getDensity(), 0.01);
}
public double getQd() {
return getPropertySum(p -> p.getQd(), 1.0);
}
}
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Yeah，搞定，终于清爽了。 :)