需要循环外返回语句的方法

Question

我在这里的方法在Eclipse上遇到问题。我要求Country如果在名为catalog的数组中找到该对象，则返回一个对象，如果未找到，则返回null。我试图遍历目录并这样做。但是，java要求我在代码的for循环之外添加return语句。但是，当我在执行该方法时在for循环外添加return语句时，它将完全忽略for循环，而仅在for循环外返回该语句。

public Country findCountry(String countryname) {

    for (int i = 0; i < catalogue.length; i++) {

        if (catalogue[i].getName() == countryname) {

            return catalogue[i];

        } else {

            return null;

        }

    }

}

编辑：在循环之前添加了foundCountry变量，并在之后返回了它。添加一个中断，并使用.equals（）比较字符串。获取一个NullPointerException。

public Country findCountry(String countryname) {

        Country foundCountry = null;

        for (int i = 0; i < catalogue.length; i++) {

            if (catalogue[i].getName().equals(countryname)) {

                foundCountry = catalogue[i];

                break;

            }

        }

        return foundCountry;

    }

Answer 1

具有流使用率的另一个版本（需要Java 8或更高版本），并且检查的版本catalogue不是null：public Country findCountry(String countryName) {&nbsp; &nbsp; if (catalogue == null) {&nbsp; &nbsp; &nbsp; &nbsp; return null;&nbsp; &nbsp; }&nbsp; &nbsp; return Arrays.stream(catalogue)&nbsp; &nbsp; &nbsp; &nbsp; .filter(country -> country.getName().equals(countryName))&nbsp; &nbsp; &nbsp; &nbsp; .findAny()&nbsp; &nbsp; &nbsp; &nbsp; .orElse(null);}

Answer 2

您可以将返回值初始化为null，并且仅在循环中找到它时才进行设置：&nbsp; &nbsp; public Country findCountry(String countryname) {&nbsp; &nbsp; &nbsp; &nbsp; // initialize a Country with null&nbsp; &nbsp; &nbsp; &nbsp; Country foundCountry = null;&nbsp; &nbsp; &nbsp; &nbsp; // try to find it&nbsp; &nbsp; &nbsp; &nbsp; for (int i = 0; i < catalogue.length; i++) {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; if (catalogue[i].getName().equals(countryname)) {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; // set it if found&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; foundCountry = catalogue[i];&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; }&nbsp; &nbsp; &nbsp; &nbsp; }&nbsp; &nbsp; &nbsp; &nbsp; // if not found, this returns null&nbsp; &nbsp; &nbsp; &nbsp; return foundCountry;&nbsp; &nbsp; }