1.反射
JAVA中反射是动态获取信息以及动态调用对象方法的一种反射机制。
Java反射就是在运行状态中,对于任意一个类,都能够知道这个类的所有属性和方法;对于任意一个对象,都能够调用它的任意方法和属性;并且能改变它的属性。而这也是Java被视为动态语言的一个关键性质。
先定义一个类,用以操作该类:
class Cat {
private String name = "秘密";
public Cat(String name) {
this.name = name;
}
public Cat() {
}
public void eat(String food) {
System.out.println(name +"正在吃"+food);
}
public void eat(String food1,String food2) {
System.out.println(name+"正在吃"+food1+","+food2);
}
}
①借助反射实例化对象
public static void testInstance() throws ClassNotFoundException, IllegalAccessException, InstantiationException{
Class catClass = Class.forName("Cat");
Cat cat = (Cat)catClass.newInstance();
}
②借助反射获取对象的属性
public static void testField() throws ClassNotFoundException, NoSuchFieldException, IllegalAccessException {
//获取类对象
Class catClass = Class.forName("Cat");
//借助类对象,获取指定的Field对象
Field field = catClass.getDeclaredField("name");
field.setAccessible(true);//专门处理private成员方式
//根据图纸修改
Cat cat = new Cat();
field.set(cat,"步步");//根据图纸修改属性
String name = (String)field.get(cat);
System.out.println(name);
}
③借助反射获取对象方法
public static void testMethod() throws ClassNotFoundException, NoSuchMethodException, InvocationTargetException, IllegalAccessException {
Class catClass = Class.forName("Cat");
//从第二个参数开始都是用来描述是哪个版本的eat
Method method = catClass.getMethod("eat",String.class);
// Method method2 = catClass.getMethod("eat",String.class,String.class);
Cat cat = new Cat();
method.invoke(cat,"鱼");
}
④借助反射调用构造方法
public static void testConstructor() throws ClassNotFoundException, NoSuchMethodException, IllegalAccessException, InvocationTargetException, InstantiationException {
Class catClass = Class.forName("Cat");
Constructor constructor = catClass.getConstructor(String.class);
constructor.setAccessible(true);
Cat cat = (Cat) constructor.newInstance("小黑");
cat.eat("猫粮");
}
2.枚举
//用于表示穷举的概念,不建议完成其他不该完成的工作
enum Sex {
MALE,
FEMALE,
UNKNOWN;
}
public class TestEnum {
public static final int Male = 0;
public static final int Female = 1;
public static final int UnKnow = 2;
public static void main(String[] args) {
/*if (Male+1 == Female) {
}*///编译可以通过但不合理
/*if (Sex.MALE+1 == Sex.FEMALE) {
}*///用枚举编译直接报错
Sex s = Sex.MALE;
System.out.println(s);
System.out.println(Arrays.toString(Sex.values()));
}
}
3.lambda
public class TestLambda {
static class Student {
public String name;
public int score;
public Student(String name, int score) {
this.name = name;
this.score = score;
}
@Override
public String toString() {
return "Student{" +
"name='" + name + '\'' +
", score=" + score +
'}';
}
}
public static void main(String[] args) {
Student[] students = {
new Student("张三",98),
new Student("李四",90),
new Student("王五",95),
new Student("赵六",92),
new Student("妮妮",99)
};
/* Arrays.sort(students, new Comparator<Student>() {
@Override
public int compare(Student o1, Student o2) {
return o1.score - o2.score;
}
});*/
//lambda表达式
Arrays.sort(students,(o1,o2) -> o1.score - o2.score);
System.out.println(Arrays.toString(students));
}
}