新手 java 在构造函数中给类中的变量赋值问题

Question

package complex_number;
import java.util.*;

public class ComplexNumber {

public static void main(String[] args){
    java.util.Scanner scanner = new java.util.Scanner(System.in);
    float m_dRealPart;
    float m_dImaginPart;

    System.out.println("Please enter the real and imaginary parts of the plural：");
    m_dRealPart=scanner.nextFloat();
    m_dImaginPart=scanner.nextFloat();
    System.out.println("\n");
    System.out.println("What kind of operation do you want to do? (1 Plus, 2 minus, 3 multiply, 4 divide)");
}

/*构造函数，ComplexNumber,将实部和虚部置0*/
public ComplexNumber(){
m_dRealPart=0;
m_dImaginPart=0;
}

    请问在构造函数的时候为什么会错？

Answer 1

这两个变量的作用域有问题，是在main入口函数中定义的，但是却在构造函数中使用，这个是不行的。你可以把两个变量定义为类级的，然后两个函数中就可以用了。
package complex_number;
import java.util.*;
public class ComplexNumber {
float m_dRealPart;
float m_dImaginPart;_**
public static void main(String[] args){
java.util.Scanner scanner = new java.util.Scanner(System.in);

System.out.println("Please enter the real and imaginary parts of the plural：");
m_dRealPart=scanner.nextFloat();
m_dImaginPart=scanner.nextFloat();
System.out.println("\n");
System.out.println("What kind of operation do you want to do? (1 Plus, 2 minus, 3 multiply, 4 divide)");

}

public ComplexNumber(){
m_dRealPart=0;
m_dImaginPart=0;
}
}