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[英]How do I call a non-static method from another class in a non-static method? (java)
[英]Entity class and encapsulation confusion - how do you call a non-static method from main()?
我正在创建一个名为“Crate”的类,它将读取以英寸为单位表示对象尺寸的整数输入文件,并输出包含每个相应项目所需的板条箱尺寸的报告。 一切似乎都很好,直到我尝试测试我的方法,因为我无法从 main() 调用它们。 尝试时,我收到一条错误消息,指出“无法从静态上下文中引用非静态方法 createReport()。”
我是初学者,所以如果有什么根本性的错误,我很乐意接受批评。 我只是好奇是否有一个简单的解决方法,以及我在静态/非静态方法方面的知识差距。
package crate;
import java.io.File;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.Scanner;
public class Crate {
private Crate[] crateList;
private int crateAmount;
private int height, width, depth, panels;
private int smallestCratePosition, smallestCrateSize;
private int largestCratePosition, largestCrateSize;
private double averageCrateSize;
public static void main(String[] args) throws IOException {
createReport();
}
public Crate() {
height = 1;
width = 1;
depth = 1;
panels = 6;
}
public void createReport() throws IOException {
Scanner infile = new Scanner(new File("ShippingSizes.txt"));
PrintWriter outfile = new PrintWriter(new File("CrateReport.txt"));
createCrateList(infile);
outfile.println("There are " + crateAmount + " crates.");
for (int i = 0; i < crateList.length; i++) {
outfile.println(i + ": height=" + crateList[i].getHeight() + ", width=" +
crateList[i].getWidth() + ", depth=" + crateList[i].getDepth() +
", panels=" + crateList[i].getPanels());
}
outfile.println("\n" + "Smallest crate is at " + smallestCratePosition +
": height=" + crateList[smallestCratePosition].getHeight() + ", width=" +
crateList[smallestCratePosition].getWidth() + ", depth=" +
crateList[smallestCratePosition].getDepth() + ", panels=" +
crateList[smallestCratePosition].getPanels());
outfile.println("Largest crate is at " + largestCratePosition + ": height," +
crateList[largestCratePosition].getHeight() + ", width=" +
crateList[largestCratePosition].getWidth() + ", depth=" +
crateList[largestCratePosition].getDepth() + ", panels=" +
crateList[largestCratePosition].getPanels());
outfile.println("Average crate size is: " + averageCrateSize);
outfile.close();
infile.close();
}
public void setCrateDimensions(Scanner scnr) {
int tempValue = scnr.nextInt();
height = tempValue/12;
if (tempValue%12 != 0)
height++;
tempValue = scnr.nextInt();
width = tempValue/12;
if (tempValue%12 != 0)
width++;
tempValue = scnr.nextInt();
depth = tempValue/12;
if (tempValue%12 != 0)
depth++;
panels = 2*((height*width)+(height*depth)+(width*depth));
}
public void createCrateList(Scanner scnr) {
crateAmount = scnr.nextInt();
for (int i = 0; i < crateAmount; i++) {
crateList[i].setCrateDimensions(scnr);
}
}
public void getSmallestCrate() {
smallestCrateSize = crateList[0].getPanels();
for (int i = 0; i < crateList.length; i++) {
if (crateList[i].getPanels() < smallestCrateSize) {
smallestCratePosition = i;
smallestCrateSize = crateList[i].getPanels();
}
}
}
public void getLargestCrate() {
largestCrateSize = crateList[0].getPanels();
for (int i = 0; i < crateList.length; i++) {
if (crateList[i].getPanels() > largestCrateSize) {
largestCratePosition = i;
largestCrateSize = crateList[i].getPanels();
}
}
}
public void getAverageCrateSize() {
double totalPanels = 0;
for (int i = 0; i < crateList.length; i++)
totalPanels += crateList[i].getPanels();
averageCrateSize = totalPanels / (double)(crateList.length);
}
public int getHeight() {
return height;
}
public int getWidth() {
return width;
}
public int getDepth() {
return depth;
}
public int getPanels() {
return panels;
}
}
我尝试在 main() 中声明 Scanner、PrintWriter、Crate[] 对象和 crateAmount 整数,但这只会导致同样的问题,因为我无法在我的方法中使用这些变量。 任何帮助将不胜感激!
因为createReport
方法与它的 Class Crate 实例相关。 您必须通过new
关键字创建一个实例,然后您可以调用它的方法createReport
。
另一种方式,如果您不想创建类的实例,则可以通过关键字static
将方法声明为静态方法。 那么该方法将在启动 jvm 时加载。
建议:你应该通过阅读书籍或其他文章来深入了解 OOP 编程
非静态方法属于类的实例,而不是类本身。 这就是您无法从main()
访问createReport()
方法的原因,因为 main 在静态范围内,而 createReport 不在。 尝试实例化类的实例并在对象上调用createReport()
。
例如:
Crate crate = new Crate();
crate.createReport();
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