Java reflection_Simple example of changing variables and methods in private

Java reflection_Simple example of changing variables and methods in private

 class DemoTest{ private String name="123"; public getName(){ system.out.println("public getName " + name); return name; } private getName2(){ system.out.println("private getName2 " + name); return name; }}

For example, change the value of name. How to change. How to change through java reflection

Let's first look at how to use reflection to call the getName method

 class<DemoTest> calzz=DemoTest.class;Constructor cons=clazz.getConstructor(new class[]{});//This is the constructor to get the class object. The object of the class whose parameters are constructed.

For example: DemoTest has a constructor method public DemoTest(String arg0,String arg1){......}

At this time, Constructor cons=clazz.getConstructor(new class[]{String.class,String.class}); the two String.cals correspond to arg0 and arg1 respectively.

Next is:

 DemoTest test=(DemoTest)cons.newInstance(new Object[]{});// Generate the corresponding object. The parameter new Object[]{} is the specific value of the parameter corresponding to the construction method. As mentioned earlier: DemoTest test=(DemoTest)cons.newInstance(new Object[]{"Li Che","Zhang San"});

Next:

 Method method=clazz.getMethod("getName",new Class[]{String.class}); method.invoke(test,new Object[]{"Wang Wu"});

At this time, you can print out the Wu Wu.

Then how to change the value of name as private.

1. Get the field first,

 Field field=clazz.getDeclaredField("name");

2. Set the accessible flag of this object to the indicated boolean value. A value of true indicates that the reflected object should cancel the Java language access check when used. A value of false indicates that the reflected object should perform Java language access checking.

 field.setAccessible(true);

3. Modify the variable value

 field.set("name","Wang Wu");

OK;

The same is true for accessing private methods.

 Method method=clazz.getDeclaredMethod("getName2"); method.setAccessible(true); method.invoke(test,new Object[]{"Wang Wu"});

Use getDeclaredFields to get private and public protected fields

If you use c.getFields(); you can only get properties of public type

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