JAVA8新特性(六)——Optional API

if(str!=null && !“”.equlas(str)) {
 
} else {
 str = “defalut”
}

Optional. ofNullable(str). orElse(“defalut”);

Optional<String> str = Optional.of("sss");
//of参数为空，抛nullPointException
//Optional<String> str1 = Optional.of(null);
//ofNullable，参数可以为空，为空则返回值为空
Optional<String> str1 = Optional.ofNullable(null);

if (str.isPresent()) {
    System.out.println(str.get());
}
if (str1.isPresent()) {
    System.out.println(str1.get());
}

//orElse
System.out.println(str.orElse("There is no value present!"));
System.out.println(str1.orElse("There is no value present!"));

//orElseGet，设置默认值
System.out.println(str.orElseGet(() -> "default value"));
System.out.println(str1.orElseGet(() -> "default value"));

try {
    //orElseThrow
    str1.orElseThrow(Exception::new);
} catch (Throwable ex) {
    //输出: No value present in the Optional instance
    System.out.println(ex.getMessage());
}

//map
Optional<String> upperName = str.map((value) -> value.toUpperCase());
System.out.println(upperName.orElse("default value"));
Optional<String> upperName1 = str1.map((value) -> value.toUpperCase());
System.out.println(upperName1.orElse("default value"));

//flatmap
upperName = str.flatMap((value) -> Optional.of(value.toUpperCase()));
System.out.println(upperName.orElse("No value found"));

//filter，参数是Predicate接口
Optional<String> newStr = str.filter((value) -> value.length() > 5);
System.out.println(newStr.orElse("str length is less than 5"));