在Java中检查一个类对象是否是另一个类对象的子类

我正在摆弄Java的反射API，并试图处理一些字段。现在我不得不识别字段的类型。字符串很简单，只需执行myField.getType().equals(String.class)。这同样适用于其他非派生类。但是如何检查派生类呢?例如，LinkedList作为List的子类。我找不到任何isSubclassOf(…)或extends(…)方法。我需要遍历所有getSuperClass()并通过自己的超类找到我的超类吗?

当前回答

/ /继承

    class A {
      int i = 10;
      public String getVal() {
        return "I'm 'A'";
      }
    }

    class B extends A {
      int j = 20;
      public String getVal() {
        return "I'm 'B'";
      }
    }

    class C extends B {
        int k = 30;
        public String getVal() {
          return "I'm 'C'";
        }
    }

/ /方法

    public static boolean isInheritedClass(Object parent, Object child) {
      if (parent == null || child == null) {
        return false;
      } else {
        return isInheritedClass(parent.getClass(), child.getClass());
      }
    }

    public static boolean isInheritedClass(Class<?> parent, Class<?> child) {
      if (parent == null || child == null) {
        return false;
      } else {
        if (parent.isAssignableFrom(child)) {
          // is child or same class
          return parent.isAssignableFrom(child.getSuperclass());
        } else {
          return false;
        }
      }
    }

//测试代码

    System.out.println("isInheritedClass(new A(), new B()):" + isInheritedClass(new A(), new B()));
    System.out.println("isInheritedClass(new A(), new C()):" + isInheritedClass(new A(), new C()));
    System.out.println("isInheritedClass(new A(), new A()):" + isInheritedClass(new A(), new A()));
    System.out.println("isInheritedClass(new B(), new A()):" + isInheritedClass(new B(), new A()));


    System.out.println("isInheritedClass(A.class, B.class):" + isInheritedClass(A.class, B.class));
    System.out.println("isInheritedClass(A.class, C.class):" + isInheritedClass(A.class, C.class));
    System.out.println("isInheritedClass(A.class, A.class):" + isInheritedClass(A.class, A.class));
    System.out.println("isInheritedClass(B.class, A.class):" + isInheritedClass(B.class, A.class));

/ /结果

    isInheritedClass(new A(), new B()):true
    isInheritedClass(new A(), new C()):true
    isInheritedClass(new A(), new A()):false
    isInheritedClass(new B(), new A()):false
    isInheritedClass(A.class, B.class):true
    isInheritedClass(A.class, C.class):true
    isInheritedClass(A.class, A.class):false
    isInheritedClass(B.class, A.class):false

2019-04-26 02:38:19

其他回答

另一个选项是instanceof:

Object o =...
if (o instanceof Number) {
  double d = ((Number)o).doubleValue(); //this cast is safe
}

2011-01-03 12:59:08

这对我来说很管用:

protected boolean isTypeOf(String myClass, Class<?> superClass) {
    boolean isSubclassOf = false;
    try {
        Class<?> clazz = Class.forName(myClass);
        if (!clazz.equals(superClass)) {
            clazz = clazz.getSuperclass();
            isSubclassOf = isTypeOf(clazz.getName(), superClass);
        } else {
            isSubclassOf = true;
        }

    } catch(ClassNotFoundException e) {
        /* Ignore */
    }
    return isSubclassOf;
}

2015-07-24 16:39:26

你需要这样的方法:

boolean isList = List.class.isAssignableFrom(myClass);

在一般情况下，List(上面)应该替换为超类和myClass应该替换为子类

从JavaDoc:

确定此class对象表示的类或接口是否与指定class参数表示的类或接口相同，或者是否是类或接口的超类或超接口。如果是，则返回true;否则返回false。如果这个Class对象表示一个基本类型，如果指定的Class参数恰好是这个Class对象，则此方法返回true;否则返回false。

参考:

Class.isAssignableFrom(类)

相关:

a)检查一个对象是否是你在编译时知道的类或接口(包括子类)的实例:

boolean isInstance = someObject instanceof SomeTypeOrInterface;

例子:

assertTrue(Arrays.asList("a", "b", "c") instanceof List<?>);

b)检查对象是否是你只在运行时才知道的类或接口(包括子类)的实例:

Class<?> typeOrInterface = // acquire class somehow
boolean isInstance = typeOrInterface.isInstance(someObject);

例子:

public boolean checkForType(Object candidate, Class<?> type){
    return type.isInstance(candidate);
}

2011-01-03 12:49:11

除了@To-kra的回答。如果有人不喜欢递归:

    public static boolean isSubClassOf(Class<?> clazz, Class<?> superClass) {
        if(Object.class.equals(superClass)) {
            return true;
        }

        for(; !Object.class.equals(clazz); clazz = clazz.getSuperclass()) {
            if(clazz.getSuperclass().equals(superClass)) {
                return true;
            }
        }

        return false;
    }

注意:没有空检查的清晰度。

2020-10-30 12:39:25