内部类（Inner Classes）、匿名内部类（Anonymous Inner Classes）和局部内部类（Local Inner Classes）是常见的语言特性。这些类为开发者提供了灵活的代码组织方式，使代码更加简洁和易读。
语法糖：通俗易懂的就是在原有语法基础上加入花活儿，通过改造编译器使得花活儿代码编译成已有代码，简化了书写，本质上.class里还是那些语法
匿名内部类:
java
public class OuterClass {
public OuterClass() {
}
public void createAnonymousClass() {
Runnable var1 = new Runnable() {
@Override
public void run() {
System.out.println("唱");
}
};
Runnable var2 = new Runnable() {
@Override
public void run() {
System.out.println("跳");
}
};
Runnable var3 = new Runnable() {
@Override
public void run() {
System.out.println("rap");
}
};
new Thread(var1).start();
Thread basketball = new Thread(() -> {
System.out.println("篮球");
});
}
}上面代码再熟悉不过了，编译后的class结构就如下，我们进行反编译这几个匿名内部类：
java
class OuterClass$1 implements Runnable {
OuterClass$1(final OuterClass this$0) {
this.this$0 = this$0;
}
public void run() {
System.out.println("唱");
}
}
java
class OuterClass$2 implements Runnable {
OuterClass$2(final OuterClass this$0) {
this.this$0 = this$0;
}
public void run() {
System.out.println("跳");
}
}
java
class OuterClass$3 implements Runnable {
OuterClass$3(final OuterClass this$0) {
this.this$0 = this$0;
}
public void run() {
System.out.println("rap");
}
}内部类：
java
public class OuterClass {
public OuterClass() {
}
public class InnerClass {
public InnerClass() {
}
public void display() {
System.out.println("内部类");
}
}
}反编译：
java
public class OuterClass$InnerClass {
public OuterClass$InnerClass(final OuterClass this$0) {
this.this$0 = this$0;
}
public void display() {
System.out.println("内部类");
}
}局部内部类：
java
public class OuterClass {
public OuterClass() {
}
public void createLocalInnerClass() {
class LocalInnerClass {
public LocalInnerClass() {
}
public void show() {
System.out.println("局部内部类");
}
}
LocalInnerClass local = new LocalInnerClass();
local.show();
}
}
反编译：
java
class OuterClass$1LocalInnerClass {
public OuterClass$1LocalInnerClass(final OuterClass this$0) {
this.this$0 = this$0;
}
public void show() {
System.out.println("局部内部类");
}
}增强for循环：
java
// 增强的for循环
public void enhancedForLoop() {
int[] numbers = {1, 2, 3, 4, 5};
for (int number : numbers) {
System.out.println("增强for循环输出: " + number);
}
}编译后： 变成for i循环了
java
public void enhancedForLoop() {
int[] numbers = new int[]{1, 2, 3, 4, 5};
int[] var2 = numbers;
int var3 = numbers.length;
for(int var4 = 0; var4 < var3; ++var4) {
int number = var2[var4];
System.out.println("增强for循环输出: " + number);
}
}Lambda表达式
java
public void lambdaExpression() {
Runnable runnable = () -> System.out.println("使用Lambda表达式运行");
runnable.run();
}反编译后：看着只是套了层括号
java
public void lambdaExpression() {
Runnable runnable = () -> {
System.out.println("使用Lambda表达式运行");
};
runnable.run();
}自动装箱与拆箱
java
public void autoBoxing() {
Integer boxed = Integer.valueOf(1024);
int unboxed = boxed;
int a=1000;
Integer b=a;
}反编译后：第一行Integer boxed = 1024;应该是编译器优化了
java
public void autoBoxing() {
Integer boxed = 1024;
int unboxed = boxed;
int a = 1000;
Integer b = Integer.valueOf(a);
}菱形操作符
java
public void diamondOperator() {
Map<String, List<Integer>> map = new HashMap<>();
map.put("键", Arrays.asList(1, 2, 3));
System.out.println("菱形操作符输出: " + map);
}反编译后：
java
public void diamondOperator() {
Map<String, List<Integer>> map = new HashMap();
map.put("键", Arrays.asList(1, 2, 3));
System.out.println("菱形操作符输出: " + map);
}try-with-resources:
java
public void tryWithResources() {
try (BufferedReader reader = new BufferedReader(new FileReader("test.txt"))) {
System.out.println("try-with-resources读取文件: " + reader.readLine());
} catch (IOException e) {
System.out.println("文件读取失败，错误信息: " + e.getMessage());
}
}
java
public void tryWithResources() {
try {
BufferedReader reader = new BufferedReader(new FileReader("test.txt"));
Throwable var2 = null;
try {
System.out.println("try-with-resources读取文件: " + reader.readLine());
} catch (Throwable var12) {
var2 = var12;
throw var12;
} finally {
if (reader != null) {
if (var2 != null) {
try {
reader.close();
} catch (Throwable var11) {
var2.addSuppressed(var11);
}
} else {
reader.close();
}
}
}
} catch (IOException var14) {
IOException e = var14;
System.out.println("文件读取失败，错误信息: " + e.getMessage());
}
}方法引用:
java
public void methodReference() {
List<String> names = Arrays.asList("张三", "李四", "王五");
System.out.println("方法引用输出:");
names.forEach(System.out::println); // 方法引用
}反编译后：帮你取了
java
public void methodReference() {
List<String> names = Arrays.asList("张三", "李四", "王五");
System.out.println("方法引用输出:");
PrintStream var10001 = System.out;
names.forEach(var10001::println);
}有迭代器的集合增强for循环
java
public void iteratorLoop() {
List<String> names = Arrays.asList("张三", "李四", "王五");
for (String name : names) {
System.out.println(name);
}
}反编译后：
java
public void iteratorLoop() {
List<String> names = Arrays.asList("张三", "李四", "王五");
Iterator var2 = names.iterator();
while(var2.hasNext()) {
String name = (String)var2.next();
System.out.println(name);
}
}