public class Bat {
  final double PI = 3.14; // 在定义时赋值
  final int i; // 因为要在构造函数中进行初始化，所以此处便不可再赋值
  final List<Bat> list; // 因为要在构造函数中进行初始化，所以此处便不可再赋值
 
  Bat() {
    i = 100;
    list = new LinkedList<Bat>();
  }
 
  Bat(int ii, List<Bat> l) {
    i = ii;
    list = l;
  }
 
  public static void main(String[] args) {
    Bat b = new Bat();
    b.list.add(new Bat());
    // b.i=25;
    // b.list=new ArrayList<Bat>();
    System.out.println("I=" + b.i + " List Type:" + b.list.getClass());
    b = new Bat(23, new ArrayList<Bat>());
    b.list.add(new Bat());
    System.out.println("I=" + b.i + " List Type:" + b.list.getClass());
  }
}

I=100 List Type:class java.util.LinkedList
I=23 List Type:class java.util.ArrayList

class Thingie {
  public static Thingie getDefaultThingie() {
    return new Thingie();
  }
}
 
public class Foo {
  private final Thingie thingie;
 
  public Foo() {
    try {
      thingie = new Thingie();
    } catch (Exception e) {
      thingie = Thingie.getDefaultThingie();//Error:The final field thingie may already have been assigned
    }
  }
}

public class Foo {
  private final Thingie thingie;
 
  public Foo() {
    Thingie tempThingie;
    try {
      tempThingie = new Thingie();
    } catch (Exception e) {
      tempThingie = Thingie.getDefaultThingie();
    }
    thingie = tempThingie;
  }
}

private final int VAL_ONE=9;
private static final int VAL_TWO=99;
public static final int VAL_THREE=999;

class Value {
  int i;
 
  public Value(int i) {
    this.i = i;
  }
}
 
public class FinalData {
  private static Random rand = new Random();
 
  private String id;
 
  public FinalData(String id) {
    this.id = id;
  }
 
  private final int i4 = rand.nextInt(20);
 
  static final int i5 = rand.nextInt(20);
 
  public String toString() {
    return id + ":" + "i4:" + i4 + ", i5=" + i5;
  }
 
  public static void main(String[] args) {
    FinalData fd1 = new FinalData("fd1");
    System.out.println(fd1);
    System.out.println("Creating new FinalData");
    FinalData fd2 = new FinalData("fd2");
    System.out.println(fd1);
    System.out.println(fd2);
  }
}

fd1:i4:6, i5=3
Creating new FinalData
fd1:i4:6, i5=3
fd2:i4:17, i5=3

class Value {
  int i;
 
  public Value(int i) {
    this.i = i;
  }
}
 
public class … {
  private Value v1=new Value(11);
  private final Value v2=new Value(22);
  private static final Value v3=new Value(33);
  …
}
 
public static void main(String[] args) {
  …
  fd1.v2.i++;// OK--Object isn't constant!
  fd1.v1=new Value(9);//OK--not final
  fd1.v2=new Value(0);//Error:Can't change reference
  fd1.v3=new Value(1);//Error:Can't change reference
  …
}

public class … {
  private final int[] a={1,2,3,4,5,6};
  …
}
 
public static void main(String[] args) {
  …
  for(int i=0;i<fd1.a.length;i++)
 fd1.a[i]++;// OK--Object isn't constant!
  fd1.a=new int[3];//Error:Can't change reference  …
}

// Not immutable -- the states array could be modified by a malicious
// callerpublic
class DangerousStates {
  private final String[] states = new String[] { "Alabama", "Alaska", "ect" };
 
  public String[] getStates() {
    return states;
  }
}

// Immutable -- returns an unmodifiable List insteadpublic
class SafeStates {
  private final String[] states = new String[] { "Alabama", "Alaska", "ect" };
 
  private final List statesAsList = new AbstractList() {
    public Object get(int n) {
      return states[n];
    }
 
    public int size() {
      return states.length;
    }
  };
 
  public List getStates() {
    return statesAsList;
  }
}

public class INClass {
  void innerClass(final String str) {
    class IClass {
      IClass() {
       System.out.println(str);
      }
    }
    IClass ic = new IClass();
  }
 
  public static void main(String[] args) {
    INClass inc = new INClass();
    inc.innerClass("Hello");
  }
}