// Java8之前：舊的寫法
Runnable runnable = new Runnable() {
 @Override
 public void run() {
   System.out.println("old run");
}
};
Thread t = new Thread(runnable);

// Java8之后：新的寫法
Runnable runnable1 = ()->{
 System.out.println("lambda run");
};
Thread t1 = new Thread(runnable1);

@FunctionalInterface
public?interface?FunctionInterfaceDemo?{
? ?void?abstractFun();
? ?default?void?fun1(){
? ? ? ?System.out.println("fun1"); ? ?
? }
? ?default?void?fun2(){
? ? ? ?System.out.println("fun2");
? } ?
}

// 編譯器會(huì)報(bào)錯(cuò)，Multiple non-overriding abstract methods found in XXX
@FunctionalInterface
public?interface?NoFunctionInterfaceDemo?extends?FunctionInterfaceDemo{
?void?abstractFun2();
}

new?Thread(()?->?System.out.println("run")).start();

public?static?String?processFile()?throws?IOException?{
? ?// Java7新增的語法，try(){}，可自動(dòng)關(guān)閉資源，減少了代碼的臃腫
? ?try(?BufferedReader?bufferedReader?=
? ? ? ?new?BufferedReader(new??FileReader("./test.txt"))){
? ? ? ?return?bufferedReader.readLine();
? }
}

@FunctionalInterface
interface?FileReadInterface{
// 這里接受一個(gè)BufferedReader對象，返回一個(gè)String對象
? ?String?process(BufferedReader?reader)?throws?IOException;
}

// 讀取一行
FileReadInterface?fileReadInterface?=?reader?->?reader.readLine();
// 讀取兩行
FileReadInterface?fileReadInterface2?=?reader?->?reader.readLine()?+?reader.readLine();

// 參數(shù)為第二步我們自己手寫的函數(shù)式接口
public static String processFile(FileReadInterface fileReadInterface) throws IOException {
       try( BufferedReader bufferedReader =
                new BufferedReader(new FileReader("./test.txt"))){
// 這里我們不再自己定義行為，而是交給函數(shù)式接口的抽象方法來處理，然后通過lambda表達(dá)式的傳入來實(shí)現(xiàn)多個(gè)行為
         return fileReadInterface.process(bufferedReader);
      }
  }

public class FileReaderDemo {
   public static void main(String[] args) throws IOException {
// 第三步：
    // lambda表達(dá)式1 傳給 函數(shù)式接口：只讀取一行
    FileReadInterface fileReadInterface = reader -> reader.readLine();
// lambda表達(dá)式2 傳給 函數(shù)式接口：只讀取兩行
    FileReadInterface fileReadInterface2 = reader -> reader.readLine() + reader.readLine();
    // 最后一步： 不同的函數(shù)式接口的實(shí)現(xiàn)，表現(xiàn)出不同的行為
       String str1 = processFile(fileReadInterface);
       String str2 = processFile(fileReadInterface2);
       System.out.println(str1);
       System.out.println(str2);
  }
// 第四步： 讀取文件方法，接受函數(shù)式接口作為參數(shù)
   public static String processFile(FileReadInterface fileReadInterface) throws IOException {
       try( BufferedReader bufferedReader =
                new BufferedReader(new FileReader("./test.txt"))){
// 調(diào)用函數(shù)式接口中的抽象方法來處理數(shù)據(jù)
         return fileReadInterface.process(bufferedReader);
      }
  }
// 第一步：
 public static String processFile() throws IOException {
       try( BufferedReader bufferedReader =
                new BufferedReader(new FileReader("./test.txt"))){
         return bufferReader.readLine();
      }
  }


}

// 第二步： 我們手寫的函數(shù)式接口
@FunctionalInterface
interface FileReadInterface{
   String process(BufferedReader reader) throws IOException;
}

@FunctionalInterface
public?interface?Function<T,?R>?{
// 都是接受一個(gè)參數(shù)，返回另一個(gè)參數(shù)
?R?apply(T?t);
}

// 簡化前
Function<Cat,?Integer>?function?=?c->c.getAge();
// 簡化后
Function<Cat,?Integer>?function2?=?Cat::getAge;