在Java中，为什么我会收到此错误：
Error: The constructor WeightIn() is undefined
Java代码：
public class WeightIn{
private double weight;
private double height;
public WeightIn (double weightIn, double heightIn){
weight = weightIn;
height = heightIn;
}
public void setWeight(double weightIn){
weight = weightIn;
}
public void setHeight(double heightIn){
height = heightIn;
}
}
public class WeightInApp{
public static void main (String [] args){
WeightIn weight1 = new WeightIn(); //Error happens here.
weight1.setWeight(3.65);
weight2.setHeight(1.7);
}
}
我定义了一个构造函数。
答案 0 :(得分：16)
将此添加到您的班级：
public WeightIn(){
}
答案 1 :(得分：4)
在此，您无法执行WeightIn weight1 = new WeightIn();，因为未定义默认构造函数。
所以你可以添加
public WeightIn(){
}
或者你可以这样做
WeightIn weight1 = new WeightIn(3.65,1.7) // constructor accept two double values
答案 2 :(得分：1)
你没有构造函数WeightIn（）。创建它或者将main方法中的参数赋给构造函数。
答案 3 :(得分：1)
WeightIn weight1 = new WeightIn();
未定义默认构造函数。请按如下方式定义： -
public weightIn()
{
}
答案 4 :(得分：1)
编译器在此行上遇到对“WeightIn()”无参数构造函数的调用：
WeightIn weight1 = new WeightIn(); //Error happens here.
编译器正在类定义中寻找匹配的构造函数，而它没有找到它。那是错误。 （你确实有一个构造函数定义：“WeightIn(double,double)”但是它有两个参数，并且不匹配。）
解决此问题的几种方法。
最简单的方法是更改main方法中的代码以传递两个参数。
WeightIn weight1 = new WeightIn( 3.65, 1.7);
//weight1.setWeight(3.65);
//weight2.setHeight(1.7);
对setWeight和setHeight方法的调用是多余的，因为已经通过构造函数方法为成员分配了值。
答案 5 :(得分：0)
首先，您应该知道一个.java文件只能有一个公共类。
您收到错误是因为您已编写参数化构造函数并访问默认构造函数。要修复此错误，请写：
WeightIn weight1 = new WeightIn(5.2, 52.2);
而不是
WeightIn weight1 = new WeightIn();
答案 6 :(得分：0)
In Java, Why am I getting this error:
Error: The constructor WeightIn() is undefined
这仅仅是因为您没有与您的类匹配的构造函数：
public class WeightIn {
...
public WeightIn (double weightIn, double heightIn){
weight = weightIn;
height = heightIn;
}
...
}
您需要添加public WeightIn() {}。
在Java中，default construct或由编译器自动生成（如果未定义）。因此，当您定义以下类时：
public class WeightIn {
private double weight;
private double height;
// didn't define a constructor.
public void setWeight(double weightIn){
weight = weightIn;
}
public void setHeight(double heightIn){
height = heightIn;
}
}
编译器将为您生成一个匹配的默认构造函数。因此，您的类隐式具有这样的默认构造函数：
public class WeightIn {
private double weight;
private double height;
// automatically generated by compiler
public WeightIn() {
// do nothing here.
}
// didn't define a constructor.
public void setWeight(double weightIn){
weight = weightIn;
}
public void setHeight(double heightIn){
height = heightIn;
}
}
当您使用以下方法实例化课程时：
WeightIn weight = new WeightIn();
一切都很好。
但是当您自己添加构造函数时，编译器将不会生成默认构造函数。因此，当您使用以下方法创建类时：
public class WeightIn {
...
// this won't automatically generated by compiler
// public WeightIn() {
// nothing to do here.
//}
public WeightIn (double weightIn, double heightIn){
weight = weightIn;
height = heightIn;
}
...
}
您将没有默认的构造函数（即public WeightIn(){}）。并使用以下内容将引发错误，因为您没有匹配的构造函数：
WeightIn weight = new WeightIn();
答案 7 :(得分：0)
花了我一段时间，但我想我终于找到了使该程序起作用的方法。
我将类分为不同的文件，并将权重类重命名为Record，以使其更加明显，而不是将所有内容都命名为权重的某种变化。我还添加了一个Output类，以使主代码尽可能保持干净和最小化。
我希望这与您希望执行的操作类似。
原始代码：“构造函数”
public class WeightIn{
private double weight;
private double height;
public WeightIn (double weightIn, double heightIn){
weight = weightIn; //needs to be : this.weight = weight
height = heightIn; //needs to be : this.height = height
}
项目：weightInApp
包装：weightInApp
类别：Record.Java
package weightInApp;
class Record
{
private double weight; //declare variables
private double height;
Record (double weight, double height) { //Parameterized Constructor method
this.weight = weight; //this is the correct way
this.height = height;
//if you want to use weightIn and/or heightIn you have to be consistent acrosss
//the whole class. I decided to drop "In" off the variables for brevity.
}
//Getters and setters
public double getWeight() {
return weight;
}
public void setWeight(double weight) {
this.weight = weight;
}
public double getHeight() {
return height;
}
public void setHeight(double height) {
this.height = height;
}
}
项目：weightInApp
包装：weightInApp
类：Output.Java
此类将设置值输出到控制台上的表。可以手动更改以添加更多数据。您还可以考虑跟踪记录的日期并将其添加到此输出中。您将需要在Record Class中为该功能添加必需的变量，getter和setter。
package weightInApp;
public class Output {
static void output (Record weightIn1, Record weightIn2)
{
int count = 0;
final Object[][] table = new Object[3][3];
table[0] = new Object[] { "Record", "Weight", "Height"};
table[1] = new Object[] { count +=1, weightIn1.getWeight(), weightIn1.getHeight() };
table[2] = new Object[] { count+=1, weightIn2.getWeight(), weightIn2.getHeight() };
for (final Object[] row : table) {
System.out.format("%15s%15s%15s\n", row);
}
}
}
项目：weightInApp
包装：weightInApp
类：Main.Java
package weightInApp;
import weightInApp.Record; //imports methods and variables from the other classes
import weightInApp.Output;
public class Main {
public static void main (String [] args){
Record weightIn1 = new Record(0,0);
//previous line of code creates a new Record object named weightIn1
//previous line of code also sets both the values of weight and height to 0.
weightIn1.setWeight(3.65); //sets weight for weightIn1
weightIn1.setHeight(1.70);//sets Height for WeightIn1
Record weightIn2 = new Record(0, 0);
weightIn2.setWeight(3.00);
weightIn2.setHeight(1.75);
//previous 3 lines are the same as above for weightIn1
//except this is for a second object named weightIn2
Output.output(weightIn1, weightIn2); //calls runs passes values to output method
}
}
示例输出
答案 8 :(得分：-2)
错误：构造函数未定义 可能的原因：
2。您可能给了错误的数据类型参数。
