Java中的反射,枚舉及lambda表達式的使用詳解

package reflectTest;
class Student{
    //私有屬性name
    private String name = "bit";
    //公有屬性age
    public int age = 18;
    //不帶參數的構造方法
    public Student(){
        System.out.println("Student()");
    }
    private Student(String name,int age) {
        this.name = name;
        this.age = age;
        System.out.println("Student(String,name)");
    }
    private void eat(){
        System.out.println("i am eat");
    }
    public void sleep(){
        System.out.println("i am pig");
    }
    private void function(String str) {
        System.out.println(str);
    } @
            Override
    public String toString() {
        return "Student{" +
                "name='" + name + '\'' +
                ", age=" + age +
                '}';
    }
}
public class test01 {
    public static void main(String[] args) {
        try {
            //通過 Class 對象的 forName() 靜態方法來獲取，用的最多，
            //但可能拋出 ClassNotFoundException 異常
            Class<?> c1 = Class.forName("reflectTest.Student");
            //直接通過 類名.class 的方式得到,該方法最為安全可靠，程序性能更高
            //這說明任何一個類都有一個隱含的靜態成員變量 class
            Class<?> c2 = Student.class;
            //通過getClass獲取Class對象
            Student student = new Student();
            Class<?> c3 = student.getClass();

            System.out.println(c1.equals(c2));
            System.out.println(c1.equals(c3));
            System.out.println(c2.equals(c3));
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }
    }
}

package reflectTest;
import java.lang.reflect.Constructor;
import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
/**
 * 通過class類的newInstance方法獲取類的實例
 */
public class ReflectClassDemo {
   public static void reflectNewInstance(){
       try {
           //獲得Class對象
           Class<?> c1 = Class.forName("reflectTest.Student");
           //創建類的實例
           Student student = (Student) c1.newInstance();
           System.out.println(student);
       } catch (ClassNotFoundException e) {
           e.printStackTrace();
       } catch (IllegalAccessException e) {
           e.printStackTrace();
       } catch (InstantiationException e) {
           e.printStackTrace();
       }
   }
    /**
     * 反射私有的構造方法
     */
    public static void reflectPrivateConstructor() {
        try {
            Class<?> c1 = Class.forName("reflectTest.Student");
            //構造方法
            Constructor<?> constructor =  c1.getDeclaredConstructor(String.class,int.class);
            //設置為true後可修改訪問權限
            constructor.setAccessible(true);
            Student student = (Student) constructor.newInstance("world",18);
            System.out.println(student);
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        } catch (NoSuchMethodException e) {
            e.printStackTrace();
        } catch (IllegalAccessException e) {
            e.printStackTrace();
        } catch (InstantiationException e) {
            e.printStackTrace();
        } catch (InvocationTargetException e) {
            e.printStackTrace();
        }
    }

    /**
     * 反射私有屬性
     */
    public static void reflectPrivateField() {
        try {
            Class<?> c1 = Class.forName("reflectTest.Student");
            Student student = (Student) c1.newInstance();
            Field field =  c1.getDeclaredField("name");
            field.setAccessible(true);
            field.set(student,"zhang");
            System.out.println(student);
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        } catch (IllegalAccessException e) {
            e.printStackTrace();
        } catch (InstantiationException e) {
            e.printStackTrace();
        } catch (NoSuchFieldException e) {
            e.printStackTrace();
        }
    }

    // 反射私有方法
    public static void reflectPrivateMethod() {
        try {
            Class<?> c1 = Class.forName("reflectTest.Student");
            Student student = (Student) c1.newInstance();
           Method method = c1.getDeclaredMethod("function",String.class);
           method.setAccessible(true);
           method.invoke(student,"我是私有的方法的參數");
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        } catch (IllegalAccessException e) {
            e.printStackTrace();
        } catch (InstantiationException e) {
            e.printStackTrace();
        } catch (NoSuchMethodException e) {
            e.printStackTrace();
        } catch (InvocationTargetException e) {
            e.printStackTrace();
        }
    }
    public static void main(String[] args) {
//        reflectNewInstance();
//        reflectPrivateConstructor();
//        reflectPrivateField();
        reflectPrivateMethod();
    }
}

public static int final RED = 1;
public static int final GREEN = 2;
public static int final BLACK = 3;

package enumTest;
public enum test01 {
    RED,BLACK,GREEN,WHITE;
    public static void main(String[] args) {
//        System.out.println(test01.BLACK);
//        System.out.println(BLACK);
        test01 te = test01.BLACK;
        switch (te) {
            case RED:
                System.out.println("red");
                break;
            case BLACK:
                System.out.println("black");
                break;
            case WHITE:
                System.out.println("white");
                break;
            case GREEN:
                System.out.println("green");
                break;
            default:
                break;
        }
    }
}

public enum test01 {
    RED,BLACK,GREEN,WHITE;
    public static void main(String[] args) {
        test01[] te = test01.values();
        for (int i = 0; i < te.length; i++) {
            System.out.println(te[i]);
        }
     }
  }

public enum test01 {
    RED,BLACK,GREEN,WHITE;
    public static void main(String[] args) {
        test01[] te = test01.values();
        for (int i = 0; i < te.length; i++) {
            System.out.println(te[i] + " --> " + te[i].ordinal());
        }
     }
  }

public enum test01 {
    RED,BLACK,GREEN,WHITE;

    public static void main(String[] args) {
        //把字符串變成對應的枚舉對象
        test01 te = test01.valueOf("RED");
        System.out.println(te);
        System.out.println(RED.compareTo(GREEN));//-2
        System.out.println(BLACK.compareTo(RED));//1
    }
  }

public enum test01 {
    //枚舉對象
    RED("red",1),BLACK(),GREEN(),WHITE();
    public String color;
    public int ordinal;
//private 加或者不加其都是私有的
   test01(String color, int ordinal) {
        this.color = color;
        this.ordinal = ordinal;
    }
    //無參構造
    test01(){
    }
}

// 1. 不需要參數,返回值為 2
() -> 2
// 2. 接收一個參數(數字類型),返回其2倍的值
x -> 2 * x
// 3. 接受2個參數(數字),並返回他們的和
(x, y) -> x + y
// 4. 接收2個int型整數,返回他們的乘積
(int x, int y) -> x * y
// 5. 接受一個 string 對象,並在控制臺打印,不返回任何值(看起來像是返回void)
(String s) -> System.out.print(s)

package lambdaTest;
@FunctionalInterface
//函數式接口
interface NoParameterNoReturn {
    //註意：隻能有一個方法
    void test();
}
//無返回值一個參數
@FunctionalInterface
interface OneParameterNoReturn {
    void test(int a);
}
//無返回值多個參數
@FunctionalInterface
interface MoreParameterNoReturn {
    void test(int a,int b);
}
//有返回值無參數
@FunctionalInterface
interface NoParameterReturn {
    int test();
}
//有返回值一個參數
@FunctionalInterface
interface OneParameterReturn {
    int test(int a);
}
//有返回值多參數
@FunctionalInterface
interface MoreParameterReturn {
    int test(int a,int b);
}
public class test01 {
    public static void main(String[] args) {
        // {} return 可以省略
        NoParameterReturn noParameterReturn = ()->{return 10;};
        int ret = noParameterReturn.test();
        System.out.println(ret);//10
        //()可以省略
        OneParameterReturn oneParameterReturn = (a) -> a;
        System.out.println(oneParameterReturn.test(10));//10
        MoreParameterReturn moreParameterReturn = (a,b) -> a+b;
        System.out.println(moreParameterReturn.test(1,2));//3
    }
    public static void main3(String[] args) {
        //()  {}  可省略
        OneParameterNoReturn oneParameterNoReturn = (a)-> System.out.println(a);
        oneParameterNoReturn.test(10);//10
        //int類型可以省略
        MoreParameterNoReturn moreParameterNoReturn = (a,b)-> System.out.println(a+b);
        moreParameterNoReturn.test(10,20);//30
    }
    public static void main2(String[] args) {
        NoParameterNoReturn noParameterNoReturn = () -> System.out.println("重寫方法");
        noParameterNoReturn.test();
    }
    public static void main1(String[] args) {
        NoParameterNoReturn noParameterNoReturn =  new NoParameterNoReturn(){
            public void test(){
                System.out.println("重寫方法");
            }
        };
        noParameterNoReturn.test();
    }
}

@FunctionalInterface
//函數式接口
interface NoParameterNoReturn {
    //註意：隻能有一個方法
    void test();
}
public static void main1(String[] args) {
        NoParameterNoReturn noParameterNoReturn =  new NoParameterNoReturn(){
            public void test(){
                System.out.println("重寫方法");
            }
        };
        noParameterNoReturn.test();
    }
}

package lambdaTest;
class Test {
    public void func(){
        System.out.println("func()");
    }
}
        public class test02 {
    public static void main(String[] args) {
        int a = 100;
        new Test(){
            @Override
            public void func() {
                System.out.println("我是內部類，且重寫瞭func這個方法！");
                System.out.println("捕獲遍歷" + a);//能捕獲到的變量，要麼是常量，要麼未發生改變過。
            }
        };
    }
}