测试数据：
代码语言：javascript复制 @Data
public static class ParentClass implements Serializable {
private String name;
}
@Data
@EqualsAndHashCode(callSuper = true)
public static class OneLevelChildClass extends ParentClass {
private String oneLevelChildName;
}
@Data
@EqualsAndHashCode(callSuper = true)
public static class TwoLevelChildClass extends OneLevelChildClass {
private String twoLevelChildName;
} @Test
public void testInstanceof() {
assertThat(null instanceof Serializable).isEqualTo(false);
/**
* 一个类的实例 instanceof 实现的接口定义、类定义、父类定义 都返回true
*/
ParentClass parentClass = new ParentClass();
assertThat(parentClass instanceof Serializable).isEqualTo(true);
assertThat(parentClass instanceof ParentClass).isEqualTo(true);
assertThat(parentClass instanceof OneLevelChildClass).isEqualTo(false);
assertThat(parentClass instanceof TwoLevelChildClass).isEqualTo(false);
OneLevelChildClass oneLevelChildClass = new OneLevelChildClass();
assertThat(oneLevelChildClass instanceof Serializable).isEqualTo(true);
assertThat(oneLevelChildClass instanceof ParentClass).isEqualTo(true);
assertThat(oneLevelChildClass instanceof OneLevelChildClass).isEqualTo(true);
assertThat(oneLevelChildClass instanceof TwoLevelChildClass).isEqualTo(false);
TwoLevelChildClass twoLevelChildClass = new TwoLevelChildClass();
assertThat(twoLevelChildClass instanceof Serializable).isEqualTo(true);
assertThat(twoLevelChildClass instanceof ParentClass).isEqualTo(true);
assertThat(twoLevelChildClass instanceof OneLevelChildClass).isEqualTo(true);
assertThat(twoLevelChildClass instanceof TwoLevelChildClass).isEqualTo(true);
}Class类的isInstance(Object obj)方法，obj是被测试的对象，如果obj是调用这个方法的class或子类或接口 的实例，则返回true。这个方法是instanceof运算符的动态等价。
代码语言：javascript复制 @Test
public void testIsInstance() {
/**
* 作用范围与instanceof相同
*/
ParentClass parentClass = new ParentClass();
assertThat(Serializable.class.isInstance(parentClass)).isEqualTo(true); assertThat(ParentClass.class.isInstance(parentClass)).isEqualTo(true);
assertThat(OneLevelChildClass.class.isInstance(parentClass)).isEqualTo(false); assertThat(TwoLevelChildClass.class.isInstance(parentClass)).isEqualTo(false);
OneLevelChildClass oneLevelChildClass = new OneLevelChildClass();
assertThat(Serializable.class.isInstance(oneLevelChildClass)).isEqualTo(true);
assertThat(ParentClass.class.isInstance(oneLevelChildClass)).isEqualTo(true);
assertThat(OneLevelChildClass.class.isInstance(oneLevelChildClass)).isEqualTo(true);
assertThat(TwoLevelChildClass.class.isInstance(oneLevelChildClass)).isEqualTo(false);
TwoLevelChildClass twoLevelChildClass = new TwoLevelChildClass();
assertThat(Serializable.class.isInstance(twoLevelChildClass)).isEqualTo(true);
assertThat(ParentClass.class.isInstance(twoLevelChildClass)).isEqualTo(true);
assertThat(OneLevelChildClass.class.isInstance(twoLevelChildClass)).isEqualTo(true);
assertThat(TwoLevelChildClass.class.isInstance(twoLevelChildClass)).isEqualTo(true);
}Class.isAssignableFrom: 当前类及子类都返回true。父类及接口返回false
例：
代码语言：javascript复制 @Test
public void testIsAssignableFrom() {
ParentClass parentClass = new ParentClass();
assertThat(parentClass.getClass().isAssignableFrom(Serializable.class)).isEqualTo(false);
/**
* 当前类及子类都返回true。父类及接口返回false
*/
assertThat(parentClass.getClass().isAssignableFrom(ParentClass.class)).isEqualTo(true);
assertThat(parentClass.getClass().isAssignableFrom(OneLevelChildClass.class)).isEqualTo(true);
assertThat(parentClass.getClass().isAssignableFrom(TwoLevelChildClass.class)).isEqualTo(true);
OneLevelChildClass oneLevelChildClass = new OneLevelChildClass();
assertThat(oneLevelChildClass.getClass().isAssignableFrom(Serializable.class)).isEqualTo(false);
assertThat(oneLevelChildClass.getClass().isAssignableFrom(ParentClass.class)).isEqualTo(false);
/**
* 当前类及子类都返回true。父类及接口返回false
*/
assertThat(oneLevelChildClass.getClass().isAssignableFrom(OneLevelChildClass.class)).isEqualTo(true);
assertThat(oneLevelChildClass.getClass().isAssignableFrom(TwoLevelChildClass.class)).isEqualTo(true);
TwoLevelChildClass twoLevelChildClass = new TwoLevelChildClass();
assertThat(twoLevelChildClass.getClass().isAssignableFrom(Serializable.class)).isEqualTo(false);
assertThat(twoLevelChildClass.getClass().isAssignableFrom(ParentClass.class)).isEqualTo(false);
assertThat(twoLevelChildClass.getClass().isAssignableFrom(OneLevelChildClass.class)).isEqualTo(false);
/**
* 当前类及子类都返回true。父类及接口返回false
*/
assertThat(twoLevelChildClass.getClass().isAssignableFrom(TwoLevelChildClass.class)).isEqualTo(true);
}System.out.println(ArrayList.class.isAssignableFrom(Object.class)); //false
System.out.println(Object.class.isAssignableFrom(ArrayList.class)); //true
System.out.println("String是Object的父类:" String.class.isAssignableFrom(Object.class)); //false
System.out.println("Object是String的父类:" Object.class.isAssignableFrom(String.class)); //true
System.out.println("Object和Object相同:" Object.class.isAssignableFrom(Object.class)); //true @Test
public void testArrayInClassMethod() {
Integer[] intTypes = {1, 2};
assertThat(intTypes.getClass().isArray()).isTrue();
assertThat(intTypes instanceof Integer[]).isTrue();
// assertThat(intTypes instanceof int[]); //会编译报错：不兼容的类型
assertThat(intTypes instanceof Object[]).isTrue();
assertThat(Integer[].class.isInstance(intTypes)).isTrue();
assertThat(Object[].class.isInstance(intTypes)).isTrue();
// assertThat(intTypes instanceof String[]).isTrue();//会编译报错：不兼容的类型
assertThat(intTypes.getClass().isAssignableFrom(Object[].class)).isFalse();
assertThat(intTypes.getClass().isAssignableFrom(Integer[].class)).isTrue();
/**
* 当前类及子类都返回true。父类及接口返回false
*/
assertThat(intTypes.getClass().isAssignableFrom(Object[].class)).isFalse();
assertThat(intTypes.getClass().isAssignableFrom(Integer[].class)).isTrue();
Object[] objects = {1, 2};
assertThat(objects instanceof Integer[]).isFalse();
assertThat(objects instanceof Object[]).isTrue();
assertThat(Integer[].class.isInstance(objects)).isFalse();//具体到抽象的为false
assertThat(Object[].class.isInstance(objects)).isTrue();
/**
* 当前类及子类都返回true。父类及接口返回false
*/
assertThat(objects.getClass().isAssignableFrom(Object[].class)).isTrue();
assertThat(objects.getClass().isAssignableFrom(Integer[].class)).isTrue();
} /**
* Determines if the specified {@code Object} is assignment-compatible
* with the object represented by this {@code Class}. This method is
* the dynamic equivalent of the Java language {@code instanceof}
* operator. The method returns {@code true} if the specified
* {@code Object} argument is non-null and can be cast to the
* reference type represented by this {@code Class} object without
* raising a {@code ClassCastException.} It returns {@code false}
* otherwise.
*
* <p> Specifically, if this {@code Class} object represents a
* declared class, this method returns {@code true} if the specified
* {@code Object} argument is an instance of the represented class (or
* of any of its subclasses); it returns {@code false} otherwise. If
* this {@code Class} object represents an array class, this method
* returns {@code true} if the specified {@code Object} argument
* can be converted to an object of the array class by an identity
* conversion or by a widening reference conversion; it returns
* {@code false} otherwise. If this {@code Class} object
* represents an interface, this method returns {@code true} if the
* class or any superclass of the specified {@code Object} argument
* implements this interface; it returns {@code false} otherwise. If
* this {@code Class} object represents a primitive type, this method
* returns {@code false}.
*
* @param obj the object to check
* @return true if {@code obj} is an instance of this class
*
* @since JDK1.1
*/
public native boolean isInstance(Object obj); /**
* Determines if the class or interface represented by this
* {@code Class} object is either the same as, or is a superclass or
* superinterface of, the class or interface represented by the specified
* {@code Class} parameter. It returns {@code true} if so;
* otherwise it returns {@code false}. If this {@code Class}
* object represents a primitive type, this method returns
* {@code true} if the specified {@code Class} parameter is
* exactly this {@code Class} object; otherwise it returns
* {@code false}.
*
* <p> Specifically, this method tests whether the type represented by the
* specified {@code Class} parameter can be converted to the type
* represented by this {@code Class} object via an identity conversion
* or via a widening reference conversion. See <em>The Java Language
* Specification</em>, sections 5.1.1 and 5.1.4 , for details.
*
* @param cls the {@code Class} object to be checked
* @return the {@code boolean} value indicating whether objects of the
* type {@code cls} can be assigned to objects of this class
* @exception NullPointerException if the specified Class parameter is
* null.
* @since JDK1.1
*/
public native boolean isAssignableFrom(Class<?> cls);https://github.com/helloworldtang/spring-boot-cookbook/blob/master/learning-demo/src/test/java/com/tangcheng/learning/reflect/TestClassAPI.java
