Java反射例题代码

迷南。 2023-07-13 15:01 101阅读 0赞

**例题**  
创建一个Example\_02类，一次声明int、float、boolean、String型得成员变量，并将他们设置为不同得访问权限。然后通过反射访问Example\_02类中的所有成员变量，将成员变量得名称和类型信息输出到控制台，并分别将各个成员变量修改前后得值输出到控制台。

public class Example_02 { 
        int i;
        public float f;
        protected boolean b;
        private String s;
    }

import java.lang.reflect.Field;
    
    public class Example_02min { 
        public static void main(String[] args) { 
            Example_02 example = new Example_02();
            Class exampleC = example.getClass(); 
            Field[] declaredFields = exampleC.getDeclaredFields();  
            for (int i = 0; i < declaredFields.length; i++) { 
                Field field = declaredFields[i]; 
                System.out.println("名称为：" + field.getName()); 
                Class fieldType = field.getType();
                System.out.println("类型为：" + fieldType);  
     
                boolean isTrue = true;
                while (isTrue) { 
                    try { 
                        isTrue = false;
                        System.out.println("修改前的值：" + field.get(example));
     
                        if (fieldType.equals(int.class)) { 
                            System.out.println("利用方法setInt()修改成员变量的值");
                            field.setInt(example, 168);
                        } else if (fieldType.equals(float.class)) {  
                            System.out.println("利用方法setFloat()修改成员变量的值");
                            field.setFloat(example, 99.9F);
                        } else if (fieldType.equals(boolean.class)) { 
                            System.out.println("利用方法setBoolean()修改成员变量的值");
                            field.setBoolean(example, true);
                        } else { 
                            System.out.println("利用方法set()修改成员变量的值");
                            field.set(example, "ZQChandson");  //可以为各种类型的成员变量赋值
                        }
                        System.out.println("修改后的值：" + field.get(example));
                    } catch (Exception e) { 
                        //String s;权限为private，需要先设置setAccessible()再修改
                        System.out.println("在设置成员变量时抛出异常，下面执行setAccessible()方法");
                        field.setAccessible(true);
                        isTrue = true;
                    }
                }
                System.out.println("---------------------------");
            }
     
     
            Field field = declaredFields[3];
            try { 
                field.set(example, "hi");
                System.out.println(field.get(example));
                field.setAccessible(false);  //修改过一次后就一直是true了
            } catch (IllegalAccessException e) { 
                e.printStackTrace();
            }
        }
    }

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**例题**  
创建一个Example\_03类，并编写四个典型得方法，然后通过反射访问，将各个方法得名称、入口参数类型、返回值类型输出。

public class Example_03 { 
        static void staticMethod() { 
            System.out.println("执行staticMethod()方法");
        }
     
        public int publicMethod(int i) { 
            System.out.println("执行publicMethod()方法");
            return i * 100;
        }
     
        protected int protectedMethod(String s, int i) throws NumberFormatException { 
            System.out.println("执行protectedMethod()方法");
            return Integer.valueOf(s) + i;
        }
     
        private String privateMethod(String... strings) { 
            System.out.println("执行privateMethod()方法");
            StringBuffer stringBuffer = new StringBuffer();
            for (int i = 0; i < strings.length; i++) { 
                stringBuffer.append(strings[i]);
            }
            return stringBuffer.toString();
     
        }
    }

import java.lang.reflect.Method;
     
    public class Example_03min { 
        public static void main(String[] args) { 
            Example_03 example = new Example_03();
            Class exampleC = example.getClass();
            Method[] declaredMethods = exampleC.getDeclaredMethods();
            for (int i = 0; i < declaredMethods.length; i++) { 
                Method method = declaredMethods[i];  
                System.out.println("名称为：" + method.getName());  
     
                System.out.println("是否允许带有可变数量的参数：" + method.isVarArgs());  
     
                System.out.println("入口参数类型依次为：");  
                Class[] parameterTypes = method.getParameterTypes();
                for (int j = 0; j < parameterTypes.length; j++) { 
                    System.out.println(" " + parameterTypes[j]);
                }
    
                System.out.println("返回值类型：" + method.getReturnType());
     
                System.out.println("可能抛出的异常：");
                Class[] exceptionTypes = method.getExceptionTypes(); 
                for (int j = 0; j < exceptionTypes.length; j++) { 
                    System.out.println(" " + exceptionTypes[j]);
                }
     
                boolean isTrue = true;
                while (isTrue) { 
      
                    try { 
                        isTrue = false;
                        if ("staticMethod".equals(method.getName())) { 
                            method.invoke(example); 
                        } else if ("publicMethod".equals(method.getName())) { 
                            System.out.println("返回值为："
                                    + method.invoke(example, 168)); 
                        } else if ("protectedMethod".equals(method.getName())) { 
                            System.out.println("返回值为："
                                    + method.invoke(example, "7", 5));
                        } else if ("privateMethod".equals(method.getName())) { 
                            Object[] parameters = new Object[]{ new String[]{ "M", "W", "Q"}}; 
                            System.out.println("返回值为："
                                    + method.invoke(example, parameters));
                        }
     
                    } catch (Exception e) { 
                        System.out.println("在执行方法时出现异常，执行下面的setAccessible()方法");
                        method.setAccessible(true);
                        isTrue = true;
                    }
                }
                System.out.println();
            }
        }
    }

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L20wXzQ2MTkzOTgy_size_16_color_FFFFFF_t_70 1]

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