【JAVA】Optional优化if判空长龙

Optional

为什么要有这个？

先来看个例子，思考一下会输出null还是报错呢？

public class TestOptional {public static void main(String[] args) {OptionTest optionTest = new OptionTest();System.out.println(optionTest.getInnerParam().getInnerInnerParam().getParam());}
}@Data
class OptionTest{private int id;private int age;private InnerParam innerParam;
}
@Data
class InnerParam{private int param;private InnerInnerParam innerInnerParam;
}
@Data
class  InnerInnerParam{private int param;private int superman;
}

输出：

Exception in thread "main" java.lang.NullPointerExceptionat com.example.demostudy.kusch.javabase.optional.TestOptional.main(TestOptional.java:18)
Process finished with exit code 1

很明显报错了。

解决这个报错很简单，加判断呗。

public class TestOptional {public static void main(String[] args) {OptionTest optionTest = new OptionTest();InnerParam innerParam = optionTest.getInnerParam();if (null!=innerParam){InnerInnerParam innerInnerParam = innerParam.getInnerInnerParam();if (null!=innerInnerParam){System.out.println(innerInnerParam.getParam());}}}
}@Data
class OptionTest{private int id;private int age;private InnerParam innerParam;
}
@Data
class InnerParam{private int param;private InnerInnerParam innerInnerParam;
}
@Data
class  InnerInnerParam{private int param;private int superman;
}

这虽然可以很好的解决，但是如果嵌套层数很深，那你是不是打算写一整页的if判断？？

Optional的使用

先看使用

public class TestOptional {public static void main(String[] args) {OptionTest optionTest = new OptionTest();Integer result = Optional.ofNullable(optionTest).map(OptionTest::getInnerParam).map(InnerParam::getInnerInnerParam).map(InnerInnerParam::getSuperman).orElse(999);System.out.println(result);}
}
@Data
class OptionTest {private int id;private int age;private InnerParam innerParam;
}
@Data
class InnerParam {private int param;private InnerInnerParam innerInnerParam;
}
@Data
class InnerInnerParam {private int param;private int superman;
}

输出：

999Process finished with exit code 0

可以看出这样不仅可以处理处理空指针异常，还可以处理，在没有值的时候所需要返回的结果。

Optional补充

public class OptionalDemo {public static void main(String[] args) {House house = new House();Television tv = new Television();tv.setCartoon("cat");house.setTelevision(tv);Boolean cartoonFlag = true;String cartoon = Optional.ofNullable(house)//类中改写Optional包装.flatMap(House::getTelevision)//没改写Optional包装.map(Television::getCartoon)//过滤，上述条件都过了，到这判断不能包含cat.filter((a) -> !tv.getCartoon().contains("cat"))//所有不符合之后要做的事.orElseGet(() -> {if (cartoonFlag) {return "niubi";}return "hahaha";});System.out.println(cartoon);}
}class House {private Television television;public void setTelevision(Television television) {this.television = television;}public Optional<Television> getTelevision() {return Optional.ofNullable(television);}
}class Television {private String cartoon;public String getCartoon() {return cartoon;}public void setCartoon(String cartoon) {this.cartoon = cartoon;}
}

注意House类中的getTelevision()方法，直接在实体类中包装optional返回，配合flatMap使用，其实区别不大。

最后附上map、flatMap、orElseGet的方法注释图。