Java出现No enclosing instance of type Test is accessible. Must qualify the allocation with an enclosin

偏执的太偏执、 2022-07-14 06:45 56阅读 0赞

最近研究LDA源代码时，里面涉及到Comparable方法的使用。以前用过这个排序方法，现在想回顾一下。以下是程序，感觉没问题啊，结果报错了：

Exception in thread "main" java.lang.Error: Unresolved compilation problem: 
        No enclosing instance of type Test is accessible. Must qualify the allocation with an enclosing instance of type Test (e.g. x.new A() where x is an instance of Test).

以下是代码程序：

package collection;
    import java.util.ArrayList;
    import java.util.Collections;
    import java.util.List;
    
    public class Test {
        /** * 根据order对User排序 */
        public  class Student implements Comparable<Student>{
            private String name;
            private Integer grade;
            public String getName() {
                return name;
            }
            public void setName(String name) {
                this.name = name;
            }
            public Integer getGrade() {
                return grade;
            }
            public void setGrade(Integer grade) {
                this.grade = grade;
            }
            public int compareTo(Student arg0) {
                return this.getGrade().compareTo(arg0.getGrade());
            }
        }
        public static void main(String[] args) {
    
            Student student1 = new Student();
            student1.setName("a");
            student1.setGrade(80);
            Student student2 = new Student();
            student2.setName("b");
            student2.setGrade(59);
            List<Student> list = new ArrayList<Student>();
            list.add(student1);
            list.add(student2);
            Collections.sort(list);
            for(Student u : list){
                System.out.println(u.getName());
            }
    
        }
    
    }

于是百度谷歌了一下相关资料。原来我写的内部类是动态的，也就是开头以**public class**开头。而主程序是public static class main。在Java中，类中的**静态方法不能直接调用动态方法**。只有将某个内部类修饰为静态类，然后才能够在静态类中调用该类的成员变量与成员方法。所以在不做其他变动的情况下，最简单的解决办法是将**public class改为public static class**.

package collection;
    
    import java.util.ArrayList;
    import java.util.Collections;
    import java.util.List;
    
    public class Test {
        /** * 根据order对User排序 */
        public static class Student implements Comparable<Student>{
            private String name;
            private Integer grade;
            public String getName() {
                return name;
            }
            public void setName(String name) {
                this.name = name;
            }
    
            public Integer getGrade() {
                return grade;
            }
            public void setGrade(Integer grade) {
                this.grade = grade;
            }
            public int compareTo(Student arg0) {
                return this.getGrade().compareTo(arg0.getGrade());
            }
        }
        public static void main(String[] args) {
    
            Student student1 = new Student();
            student1.setName("a");
            student1.setGrade(80);
            Student student2 = new Student();
            student2.setName("b");
            student2.setGrade(59);
            List<Student> list = new ArrayList<Student>();
            list.add(student1);
            list.add(student2);
            Collections.sort(list);
            for(Student u : list){
                System.out.println(u.getName());
            }
    
        }
    
    }

再次运行，发现没问题了。