Question

我正在学习java，在课堂上我们开始使用多个类.... 我有一个带有默认构造函数的employee类。在其中我有变量的默认值。我遇到的问题是没有使用默认构造函数中的变量值，所以我在变量下得到黄色下划线。有人可以引导我朝着正确的方向前进。

package week2;

import java.text.NumberFormat;

public class Employee {

    //Instance Variables
    private String firstName = "", lastName = "";
    private char gender = 'U';
    private int dependents = 0;
    private double annualSalary = 0;

    //Default Employee Constructor 
    public Employee() {
        String firstName = "not given";
        String lastName = "not given";
        char gender = 'U';
        int dependents = 0;
        double annualSalary = 20000;
    } //End of default Employee Constructor

    //Employee Constructor with variables
    public Employee(String firstName, String lastName, char gender, int dependents, double salary) {
        this.firstName = firstName;
        this.lastName = lastName;
        this.gender = gender;
        this.dependents = dependents;
        this.annualSalary = salary;
    } //End of Overloaded Employee Constructor

    //Calculate Pay
    public double annualSalary() {
        return (getAnnualSalary() / 52);
    } //End Calculate Pay

    //Display Employee
    public void displayEmployee() {
        NumberFormat nf = NumberFormat.getCurrencyInstance();

        System.out.println("First Name: \t" + this.firstName);
        System.out.println("Last Name: \t" + this.lastName);
        System.out.println("Gender: \t" + this.gender);
        System.out.println("Dependents: \t" + this.dependents);
        System.out.println("Annual Salary: \t" + nf.format(this.annualSalary));

        System.out.println("Weekly Pay: \t" + nf.format(annualSalary()));
    } //End Display Employee


    //Getters and Setters
    //Get-Set firstName
    public String getFirstName() {
        return firstName;
    }
    public void setFirstName(String firstName) {
        this.firstName = firstName;
    }

    //Get-Set lastName
    public String getLastName() {
        return lastName;
    }
    public void setLastName(String lastName) {
        this.lastName = lastName;
    }

    //Get-Set Gender
    public char getGender() {
        return gender;
    }
    public void setGender(char gender) {
        this.gender = gender;
    }

    //Get-Set dependents
    public int getDependents() {
        return dependents;
    }
    public void setDependents(int dependents) {
        this.dependents = dependents;
    }

    //Get-Set annualSalary
    public double getAnnualSalary() {
        return annualSalary;
    }
    public void setAnnualSalary(double annualSalary) {
        this.annualSalary = annualSalary;
    }
}

Answer 1

您正在默认构造函数中创建local variables。删除声明，它将为类级变量赋值。

//Default Employee Constructor 
public Employee() {
    firstName = "not given";
    lastName = "not given";
    gender = 'U';
    dependents = 0;
    annualSalary = 20000;
} //End of default Employee Constructor

注意：黄色表示警告。在你的情况下，它提示你正在创建局部变量并为其赋值，这在构造函数中没有使用，局部变量在构造函数外是不可见的。

如果没有使用相同名称定义其他局部变量，则可以使用this.firstName或firstName。（您可以在默认构造函数中使用这两种方法）

如果使用相同的名称定义某个局部变量，则firstName引用局部变量，this.firstName引用类级别变量。（您可以在参数化构造函数中看到）

Answer 2

no-arg构造函数声明了新变量，它们被初始化但未被使用，正如编译器所说。请注意，这些变量不是类中的字段。

public Employee() {
    //this is a local variable in the method
    String firstName = "not given";
    //this variable is not the same as this:
    this.firstName = "not given";
    //same for other variables
}

这种情况有两种解决方案：

删除局部变量的所有声明并改为使用字段：

public Employee() {
    this.firstName = "not given";
    //...
}

使用this()并使用字段的初始值调用其他构造函数：

public Employee() {
    this("not given", "not given", 'U', 0, 2000);
}

Answer 3

这里你需要明确的概念是变量的范围，在您的默认构造函数

中

 //Default Employee Constructor 
public Employee() {
    String firstName = "not given";
    String lastName = "not given";
    char gender = 'U';
    int dependents = 0;
    double annualSalary = 20000;
} //End of default Employee Constructor

声明的变量仅在此构造函数中具有范围，它们与在类的开头声明的实例变量不同。因此，这些变量不会在任何地方使用，因此编译器警告。

未使用的局部变量的值

3 个答案: