自定义泛型：extends,super关键字的使用
1.泛型类的使用 public class ResponseResult<T> {}
2.泛型方法的使用 public static <T extends String> T concat(T... ts) {}
3.泛型接口的使用 public interface StringBufferInterface<T extends String> {}
4.泛型关键字介绍 Fan<?>、 Fan<? extends A>、 Fan<? super A1>、 Fan<Object>
1.泛型类的使用：比较常见的接口响应数据封装 ResponseResult.java
package pers.li.genericity.$1genericclass.practise;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;
public class ResponseResult<T> {
private T data;
private String msg;
private int code;
public ResponseResult(T data, String msg, int code) {
this.data = data;
this.msg = msg;
this.code = code;
}
public ResponseResult(T data) {
this.code = 200;
this.data = data;
}
public ResponseResult() {
this.code = 200;
}
public T getData() {
return data;
}
public void setData(T data) {
this.data = data;
}
public String getMsg() {
return msg;
}
public void setMsg(String msg) {
this.msg = msg;
}
public int getCode() {
return code;
}
public void setCode(int code) {
this.code = code;
}
public static void main(String[] args) throws JsonProcessingException {
ResponseResult<String> stringResponseResult = new ResponseResult<>();
System.err.println(new ObjectMapper().writeValueAsString(stringResponseResult));
}
}
2.泛型方法的使用：简单示例字符串拼接
package pers.li.genericity.$1genericmethod.practise;
public class dataDeal {
public static <T extends String> T concat(T... ts) {
StringBuffer stringBuffer = new StringBuffer();
for (String s:ts
) {
stringBuffer.append(s);
}
return (T) stringBuffer.toString();
}
public static void main(String[] args) {
System.err.println(dataDeal.concat("1","2"," ","3"));
}
}
3.泛型接口的使用：简单示例字符串拼接
package pers.li.genericity.$1genericinterface.practise;
public interface StringBufferInterface<T extends String> {
public T concat (T... t2);
}
class TestStringBuffer implements StringBufferInterface<String>{
@Override
public String concat(String... t2) {
StringBuffer stringBuffer = new StringBuffer();
for (String s:t2
) {
stringBuffer.append(s);
}
return stringBuffer.toString();
}
public static void main(String[] args) {
TestStringBuffer test = new TestStringBuffer();
String add = test.concat("1","2");
StringBufferInterface<String> test2 = new TestStringBuffer();
String add2 = test2.concat("1","2");
System.err.println(add+"|"+add2);
}
}
4.泛型关键字对比介绍：
package pers.li.genericity.$2limits.practise;
//定义父类
abstract class A {
private int s;
public int getS() {
return s;
}
public void setS(int s) {
this.s = s;
}
public abstract void thisName();
}
//定义子类A1
class A1 extends A {
@Override
public void thisName() {
System.err.println("this is A1");
}
}
//定义A1的子类A11
class A11 extends A1 {
@Override
public void thisName() {
System.err.println("this is A11");
}
}
//定义子类A2
class A2 extends A {
@Override
public void thisName() {
System.err.println("this is A2");
}
}
//定义泛型类
class Fan<T>{
private T fan1;
private T fan2;
public T getFan1() {
return fan1;
}
public void setFan1(T fan1) {
this.fan1 = fan1;
}
public T getFan2() {
return fan2;
}
public void setFan2(T fan2) {
this.fan2 = fan2;
}
public Fan(T fan1, T fan2) {
this.fan1 = fan1;
this.fan2 = fan2;
}
public Fan() {
this.fan1 = null;
this.fan2 = null;
}
}
public class Test {
public static void main(String[] args) {
//？号表示任意类型，即Object类型，所以取值需要强转才能调用方法，放值（即set方法）由于不确定类型，所以会报错
Fan<?> fan = new Fan(new A1(),new A2());
Object fan1 = fan.getFan1();
A1 a = (A1)fan1;
a.thisName();
// fan.setFan1(new A1());
System.err.println("? super A1只能存放A1及其子类对象并且不能get，因为不知道放进去的对象是哪个+++++++++++++++++++++++++++++===");
//只能存放A1及其子类对象并且不能get，因为不知道放进去的对象是哪个，可以通过强制转换获取结果
Fan<? super A1> fan2 = new Fan<A>();
fan2.setFan1(new A1());
fan2.setFan2(new A11());
Object fan11 = fan2.getFan1();
A1 ss = (A1)fan11;
ss.thisName();
// A fan11 = fan2.getFan1();
System.err.println("? extends A只能取值不能放值,因为T必须是继承于A的子类，放值时无法知道到底是哪个子类+++++++++++++++++++++++++++++===");
Fan<? extends A> fan3 = new Fan(new A1(),new A2());
fan3.getFan1().thisName();
fan3.getFan2().thisName();
/* fan3.setFan2(new A1());
fan3.setFan2(new A2());
fan3.setFan2(new A() {
@Override
public void thisName() {
}
});*/
System.err.println("真实泛型========================================");
Fan<A> fan4 = new Fan(new A1(),new A2());
fan4.getFan1().thisName();
fan4.getFan2().thisName();
fan4.setFan2(new A2());
}
}
