java8新特性学习-接口扩展

本文转自：http://www.jb51.net/article/48304.htm

1. 首先我们编写一个接口:Formula.java

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   public interface Formula { double calculate(int a); //这里jdk7这么写不会报编译错误 default double sqrt(int a){ return Math.sqrt(a); } }

2. 然后编写一个实现类：FormulaImpl.java

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   public class FormulaImpl implements Formula { @Override public double calculate(int a) { return sqrt(a*100); } public static void main(String[] args) { Formula formula = new Formula() { @Override public double calculate(int a) { return sqrt(a * 100); } }; formula.calculate(100); // 100.0 formula.sqrt(16); // 4.0 System.out.println(formula.calculate(100)); System.out.println(formula.sqrt(16)); } }

3. 注意上面的实现类里的main方法中的调用

4. 运行后jdk7会抛异常

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   Exception in thread "main" java.lang.UnsupportedClassVersionError: com/java/demo/FormulaImpl : Unsupported major.minor version 52.0 at java.lang.ClassLoader.defineClass1(Native Method) at java.lang.ClassLoader.defineClass(ClassLoader.java:800) at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142) at java.net.URLClassLoader.defineClass(URLClassLoader.java:449) at java.net.URLClassLoader.access$100(URLClassLoader.java:71) at java.net.URLClassLoader$1.run(URLClassLoader.java:361) at java.net.URLClassLoader$1.run(URLClassLoader.java:355) at java.security.AccessController.doPrivileged(Native Method) at java.net.URLClassLoader.findClass(URLClassLoader.java:354) at java.lang.ClassLoader.loadClass(ClassLoader.java:425) at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:308) at java.lang.ClassLoader.loadClass(ClassLoader.java:358) at sun.launcher.LauncherHelper.checkAndLoadMain(LauncherHelper.java:482)

5. 运行后jdk8则正常输出

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   100.0 4.0