Thinking In Java琐碎知识点摘要(一)

1、在C和C++中将一个较大作用域的变量“隐藏”起来的做法，在Java里不允许

{
  int x=0;
  {
    int x=1;//illegal
  }
}

import java.util.Random;
public class RandomTest {
public static void main(String[] args) {
//设置了种子(48位)，则每次生成相同的伪随机序列
Random r=new Random(23);
int j=r.nextInt(100);
int i=r.nextInt();
boolean v=r.nextBoolean();
print(j);
print(i);
print(v);
}
public static  void print(Object obj){
System.out.println(obj);
}
}

5、equals方法并不是判断两个对象的值相等，对象的值如何相等？equals方法是Object类提供的一个实例方法， 这个方法判断两个对象是否相等的标准和==没有区别（对于基本类型变量，且都是数值型，则只要两个变量的值相等，即返回true;对于引用类型变量，只有指向同一个对象时才返回true）String类已经重写了equals方法。

public class Test4 {
public static void main(String[] args) {
int i=-1;
print("i:"+Integer.toBinaryString(i)+" "+i);
i>>>=10;
print("i无符号右移10位:"+Integer.toBinaryString(i)+" "+i);//若计算结果为0001111则会省略前面的所有0
i>>=4;
print("i右移10位:"+Integer.toBinaryString(i)+" "+i);
i<<=4;
print("i左移10位:"+Integer.toBinaryString(i)+" "+i);
}
public static  void print(Object obj){
System.out.println(obj);
} }

public class Test {
static String ternary (int i){
return i<10?"i<10":"i>=10";
}
static String ifelse (int i){
if(i<10){
return "i<10";
}else{
return "i>=10";
}
}
static void print(Object obj){
System.out.println(obj);
}

public static void main(String[] args) {
print("ifelse():"+ifelse(11));
print("ternary():"+ternary(11));
}
}

 // 例程1: 
public class Test5 {
public static void main(String[] args) {
Random rand=new Random(47);
float f[]=new float[10];
for(int i=0;i<10;i++){
f[i]=rand.nextFloat();
}
int i=0;
for(float x:f){
System.out.println("x["+(i++)+"]="+x);
}
}
}

//例程2:
public class Test {
public static void main(String[] args) {
for(char x:"niao peng".toCharArray()){
System.out.println(x+" ");
}
}
}

public class Test {
public static void main(String[] args) {
int i = 0;
outer: while (true) {
System.out.println("Outer while loop");
while (true) {
i++;
System.out.println("i=" + i);
if (i == 1) {
System.out.println("Continue");
continue;
}
if (i == 3) {
System.out.println("continue outer");
continue outer;
}
if (i == 5) {
System.out.println("break");
break;
}
if(i==7){
System.out.println("break outer");
break outer;
}
}
}
}
}

switch(integral-selector){
       case integral-value1:statement;break;
       case integral-value1:statement;break;
       ...
       default:statement;
    }

public class TestFinalize {
private static TestFinalize tf=null;
public static void main(String[] args) throws InterruptedException {
new TestFinalize ();
System.gc();
Thread.sleep(4000);//这句话不能少,虽然显式调用了System.gc(),但是系统没有立即执行,程序暂停时才执行了垃圾回收
tf.showInfo();
}

public void finalize() {
tf=this;
}
public void showInfo(){
System.out.println("showInfo() has been called!");
}
}

public class Test {
public static void main(String[] args) {
House h = new House();
h.print();
}
}
class Window {
Window(int a) {
System.out.println("Window(" + a + ")");
}
}
class House {
Window window1 = new Window(1);
public House() {
System.out.println("House");
window3 = new Window(33);
}
Window window2 = new Window(2);
void print() {
System.out.print("zpc");
}
Window window3 = new Window(3);
}

static {
  int i=0;
  System.out.println("initialized");
}//该块只执行一次，即该类加载时，因此static修饰的初始化块总是普通块先执行

{
 int i=0;
  System.out.println("initialized");
}//每次实例化该类都执行

  Integer[] b=new Integer[]{
        new Integer(1),new Integer(2),3,
      };

public class Test {
static void f(int require,String... args){
System.out.print("require:"+require);
for(String s:args){
System.out.print(" "+s);
}
System.out.println();
}

public static void main(String[] args) {
f(1,"one");
f(2,"one","two");
f(0);
}
}

  public enum SeasonEnum {
      SPRING,SUMMER,FALL,WINTER;
    }

public enum SeasonEnum {
SPRING("春天"),SUMMER("夏天"),FALL("秋天"),WINTER("冬天");
private String season;
private SeasonEnum(String season){
this.season=season;
}
public String getSeason(){
return this.season;
}

public static void main(String[] args){
SeasonEnum se=Enum.valueOf(SeasonEnum.class, "FALL");//SeasonEnum se=FALL;
System.out.println(se.getSeason());
se.season="春天";
System.out.println(se.getSeason());
}
}

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Thinking In Java琐碎知识点摘要(一)

原文：http://blog.csdn.net/hellozpc/article/details/23128025