// code goes here
getmeout:{
for (int i = 0; i < N; ++i) {
for (int j = i; j < N; ++j) {
for (int k = j; k < N; ++k) {
//do something here
break getmeout;
}
}
}
}
public static <A, B extends Collection<A> & Comparable<B>>
boolean foo(B b1, B b2, A a) {
return (b1.compareTo(b2) == 0) || b1.contains(a) || b2.contains(a);
}
public class App {
public App(String name) { System.out.println(name + "'s constructor called"); }
static { System.out.println("static initializer called"); }
{ System.out.println("instance initializer called"); }
static { System.out.println("static initializer2 called"); }
{ System.out.println("instance initializer2 called"); }
public static void main( String[] args ) {
new App("one");
new App("two");
}
}
执行main方法将显示:
static initializer called
static initializer2 called
instance initializer called
instance initializer2 called
one's constructor called
instance initializer called
instance initializer2 called
two's constructor called
我想，如果您有多个构造函数并且需要通用代码，那么这些将很有用
它们还提供了初始化类的语法糖:
List<Integer> numbers = new ArrayList<Integer>()\{\{ add(1); add(2); }};
Map<String,String> codes = new HashMap<String,String>()\{\{
put("1","one");
put("2","two");
}};
public static void doSomething() {
try {
//Normally you would have code that doesn't explicitly appear
//to throw exceptions so it would be harder to see the problem.
throw new RuntimeException();
} finally {
return;
}
}
public class Example
{
public static void main(String[] Args)
{
int a = 5;
Integer b = a; // Box!
System.out.println("A : " + a);
System.out.println("B : " + b);
}
}
package package.name;
public class util {
private static void doStuff1(){
//the end
}
private static String doStuff2(){
return "the end";
}
}
然后像这样使用它。
import static package.name.util.*;
public class main{
public static void main(String[] args){
doStuff1(); // wee no more typing util.doStuff1()
System.out.print(doStuff2()); // or util.doStuff2()
}
}
import static java.lang.Math.*;
import static java.lang.System.out;
public class HelloWorld {
public static void main(String[] args) {
out.println("Hello World!");
out.println("Considering a circle with a diameter of 5 cm, it has:");
out.println("A circumference of " + (PI * 5) + "cm");
out.println("And an area of " + (PI * pow(5,2)) + "sq. cm");
}
}
public class Foo {
private int bar;
public Foo() {
setBar(17);
}
private void setBar(int bar) {
this.bar=bar;
}
public int getBar() {
return bar;
}
public String toString() {
return "Foo[bar="+bar+"]";
}
}
执行这个程序…
import java.lang.reflect.*;
public class AccessibleExample {
public static void main(String[] args)
throws NoSuchMethodException,IllegalAccessException, InvocationTargetException, NoSuchFieldException {
Foo foo=new Foo();
System.out.println(foo);
Method method=Foo.class.getDeclaredMethod("setBar", int.class);
method.setAccessible(true);
method.invoke(foo, 42);
System.out.println(foo);
Field field=Foo.class.getDeclaredField("bar");
field.setAccessible(true);
field.set(foo, 23);
System.out.println(foo);
}
}
String s = "";
for (int i = 0 ; i < 1000 ; ++i)
s += " " + i; // Really an Object instantiation & 3 method invocations!
可以(应该)在你的代码中重写为:
StringBuilder buf = new StringBuilder(); // Empty buffer
for (int i = 0 ; i < 1000 ; ++i)
buf.append(' ').append(i); // Cut out the object instantiation & reduce to 2 method invocations
String s = buf.toString();
public class Slow {
/** Loop counter; initialized to 0. */
private long i;
public static void main( String args[] ) {
Slow slow = new Slow();
slow.run();
}
private void run() {
while( i++ < 10000000000L )
;
}
}
$ time java Slow
Real 0m15.397s
$ time java Slow
Real 0m20.012s
$ time java Slow
Real 0m18.645s
平均:18.018秒
public class Fast {
/** Loop counter; initialized to 0. */
private long i;
public static void main( String args[] ) {
Fast fast = new Fast();
fast.run();
}
private void run() {
long i = getI();
while( i++ < 10000000000L )
;
setI( i );
}
private long setI( long i ) {
this.i = i;
}
private long getI() {
return this.i;
}
}
$ time java Fast
Real 0m12.003s
$ time java Fast
Real 0m9.840
$ time java Fast
Real 0m9.686
Map<String, List<String>> anagrams = new HashMap<String, List<String>>();
// Can now be replaced with this:
Map<String, List<String>> anagrams = new HashMap<>();
Integer a = 1;
Integer b = 1;
Integer c = new Integer(1);
Integer d = new Integer(1);
Integer e = 128;
Integer f = 128;
assertTrue (a == b); // again: this is true!
assertFalse(e == f); // again: this is false!
assertFalse(c == d); // again: this is false!
public interface SomeInterface {
void doSomething(Object o);
}
public abstract class RuntimeCheckingTemplate<T> {
private Class<T> clazz;
protected RuntimeChecking(Class<T> clazz) {
this.clazz = clazz;
}
public void doSomething(Object o) {
if (clazz.isInstance(o)) {
doSomethingWithGeneric(clazz.cast(o));
} else {
// log it, do something by default, throw an exception, etc.
}
}
protected abstract void doSomethingWithGeneric(T t);
}
public class ClassThatWorksWithStrings extends RuntimeCheckingTemplate<String> {
public ClassThatWorksWithStrings() {
super(String.class);
}
protected abstract void doSomethingWithGeneric(T t) {
// Do something with the generic and know that a runtime exception won't occur
// because of a wrong type
}
}
String input = "1 fish 2 fish red fish blue fish";
Scanner s = new Scanner(input).useDelimiter("\\s*fish\\s*");
System.out.println(s.nextInt());
System.out.println(s.nextInt());
System.out.println(s.next());
System.out.println(s.next());
s.close();
