Question

我想打印出国家名称及其分类（如代码末尾所示）。但是，if语句不起作用。我尝试将它从构造函数中删除，但这不起作用，当我在我的main方法中尝试它时无论如何都不会工作，因为变量是在类Country中定义的。所以我想问一下，我如何使用这个if语句进行分类。

public class Exercise {


public static void main(String[] args){
    Country Sweden = new Country("Sweden", 498000000000l,10000000);
    Sweden.representcountry();
}

public static class Country{
    String name;
    long GDP;
    int population;
    int GDPCapita;

    String classification;

    public Country(String name, long GDP, int population){
        this.name = name;
        this.GDP = GDP;
        this.population = population;
        GDPCapita = (int) (this.GDP / this.population);
    }

    // Getters and Setters

    /*
     if(GDPCapita >= 10000){
        classification = "Developed country";
    }
    else {
        classification = "Developing country";
    }
    */


    final String END_OF_LINE = System.lineSeparator();
    public String representcountry(){
        System.out.println(this.name + ":" + END_OF_LINE // + classification
                + "Population: "  +  + this.population + END_OF_LINE
                + "GDP: " + this.GDP + END_OF_LINE
                + GDPCapita + " per capita");
        return "";
    }
}
}

Answer 1

你这样做：

public Country(String name, long GDP, int population){
    this.name = name;
    this.GDP = GDP;
    this.population = population;
    GDPCapita = (int) (this.GDP / this.population);
    if(GDPCapita >= 10000){
        classification = "Developed country";
    }else {
        classification = "Developing country";
    }
}

通过使用三元运算符你可以替换if / else，他更短，但你需要理解并喜欢它，这只是一个提示：

classification = GDPCapita >= 10000 ? "Developed country" : "Developing country";

Answer 2

为什么你在任何地方使用关键字＆＃34; this。＆＃34;除了GDPCapita和分类？

public Country(String name, long GDP, int population){
// Getters and Setters

    this.name = name;
    this.GDP = GDP;
    this.population = population;
    this.GDPCapita = (int) (this.GDP / this.population);
    if(this.GDPCapita >= 10000){
        this.classification = "Developed country";
    }
    else {
        this.classification = "Developing country";
    }
}

Java：我如何使用这个if-else语句（在构造函数中）？

2 个答案: