Java笔记-反射机制(二)

操作类成员的类

 java.lang.reflect.Member

操作字段

 java.lang.reflect.Field

操作方法

 java.lang.reflect.Method

操作构造器

 java.lang.reflect.Constructor

实际操作

获取字段类型

public class Main {

    public static String abc = "123";
    private static List<String> a;

    public static void main(String[] args) throws NoSuchFieldException {
        Class c = Main.class;
        Field field = c.getField("abc");
        Field field1 = c.getDeclaredField("a");

        System.out.println(field.getType());
        System.out.println(field.getGenericType());

        System.out.println();

        System.out.println(field1.getType());
        System.out.println(field1.getGenericType());
    }
}

class java.lang.String
class java.lang.String

interface java.util.List
java.util.List<java.lang.String>

获取字段修饰符

public class Main {
    public static int a = 1;
    public static void main(String[] args) throws NoSuchFieldException {
        Class c = Main.class;
        Field field = c.getField("a");
        System.out.println(Modifier.isPublic(field.getModifiers()));
        System.out.println(Modifier.isStatic(field.getModifiers()));
    }
}

读写字段值

    private static int a = 1;

    public static void main(String[] args) throws NoSuchFieldException, IllegalAccessException {
        Class c = Main.class;
        Field field = c.getDeclaredField("a");
        int b = field.getInt(Main.class);
        System.out.println(b);
        field.setInt(Main.class, 2);
        System.out.println(a);
        field.setFloat(Main.class, (float) 1.1);   // 报异常
    }

操作方法和构造器

构造器创建实例

public class Main {

    public Main() {
    }

    public static void main(String[] args) throws IllegalAccessException, InvocationTargetException, InstantiationException {
        Class c = Main.class;
        Constructor[] ctors = c.getConstructors();
        Constructor ctor = null;
        for (int i = 0; i < ctors.length; i++) {
            ctor = ctors[i];
            if (ctor.getGenericParameterTypes().length == 0)     // 需要找到默认构造函数创建实例
                break;
        }

        System.out.println(ctor.newInstance().getClass().getCanonicalName());
    }
}

结尾