java - 获取 FontMetrics StackOverflowError

Question

运行以下代码:

import java.awt.Font;
import java.awt.FontMetrics;

public class MetricsTest {

    public static void main(String[] args) {
                Font myFontTest=new Font("Arial", Font.PLAIN, 11);
                FontMetrics metrics  = new FontMetrics(myFontTest) {};
                int characterWidth=metrics.charWidth('A');
                System.out.println(characterWidth);
    }
}

产生这个错误:

线程“main”中的异常 java.lang.StackOverflowError

在 java.awt.FontMetrics.getWidths(FontMetrics.java:430)

在 java.awt.FontMetrics.charWidth(FontMetrics.java:333)

在 java.awt.FontMetrics.getWidths(FontMetrics.java:430)

在 java.awt.FontMetrics.charWidth(FontMetrics.java:333)

在 java.awt.FontMetrics.getWidths(FontMetrics.java:430)

等等....

为什么？

Answer 1

来自 the doc :

Note to subclassers: Since many of these methods form closed, mutually recursive loops, you must take care that you implement at least one of the methods in each such loop to prevent infinite recursion when your subclass is used. In particular, the following is the minimal suggested set of methods to override in order to ensure correctness and prevent infinite recursion (though other subsets are equally feasible):

这个:

FontMetrics metrics  = new FontMetrics(myFontTest) {};

定义了一个没有覆盖任何方法的子类，因此出现了您所看到的行为。