练习1:
package JAVA5;
public class E01 {
String s;
public static void main(String[] args) {
E01 s1 = new E01();
System.out.println(s1.s);
}
}
练习2:
package JAVA5;
public class E01 {
String s1 = "a";
String s2;
E01(String s2i){
s2 = s2i;
}
E01(){
System.out.println("b");
}
public static void main(String[] args) {
E01 s = new E01("ni");
E01 s4 = new E01();
System.out.println(s.s1);
System.out.println(s.s2);
}
}
练习3:
package JAVA5;
public class E03 {
E03(){
System.out.println("打印一条消息");
}
public static void main(String[] args) {
E03 s = new E03();
}
}
练习4:
package JAVA5;
public class E03 {
E03(){
System.out.println("打印一条消息");
}
E03(String s){
String s2 = s;
System.out.println(s2);
}
public static void main(String[] args) {
E03 s = new E03();
E03 s1 = new E03("你好");
}
}
练习5:
package JAVA5;
class Dog{
public void bark(int barking){
System.out.println("Barking");
}
public void bark(double big){
System.out.println("Big");
}
}
public class E05Dog {
public static void main(String[] args) {
Dog dog = new Dog();
dog.bark(1);
dog.bark(1.0);
}
}
练习6:
package JAVA5;
class Dog{
public void bark(int barking,double big){
System.out.println("Barking");
}
public void bark(double big,int barking){
System.out.println("Big");
}
}
public class E05Dog {
public static void main(String[] args) {
Dog dog = new Dog();
dog.bark(1,1.0);
dog.bark(1.0,1);
}
}
练习7:
package JAVA5;
class Dog2{}
public class E07 {
public static void main(String[] args) {
Dog2 dog = new Dog2();
}
}
练习8:
package JAVA5;
public class E08 {
void bigdog(){
bigbigdog();
this.bigbigdog();
}
void bigbigdog(){
System.out.println("bigbigdog() called");
}
public static void main(String[] args) {
new E08().bigdog();
}
}
练习9:
package JAVA5;
public class E09 {
public E09(int i){
this("i = " + i);
}
public E09(String s){
System.out.println("s = " + s);
}
public static void main(String[] args) {
new E09("String call");
new E09(47);
}
}
练习10:
package JAVA5;
public class E10 {
protected void finalize(){
System.out.println("called");
}
public static void main(String[] args) {
new E10();
}
}
练习11:
package JAVA5;
public class E10 {
protected void finalize(){
System.out.println("called");
}
public static void main(String[] args) {
new E10();
System.gc();
System.runFinalization();
}
}
练习12:
package JAVA5;
class Tank{
static int counter;
int id = counter++;
boolean full;
public Tank(){
System.out.println("Tank " + id + " created");
full = true;
}
public void empty(){full = false;}
protected void finalize(){
if (full)
System.out.println("Error: tank " + id + " must be empty at cleanup");
else
System.out.println("Tank " + id + " cleaned up OK");
}
public String toString(){return "Tank " + id;}
}
public class E12 {
public static void main(String[] args) {
new Tank().empty();
new Tank();
System.gc();
System.runFinalization();
}
}
练习13:
package JAVA5;
public class E13 {
public static void main(String[] args) {
System.out.println("Exercise left to reader");
}
}
练习14:
package JAVA5;
public class E14 {
static String s1 = "Initialized at definition";
static String s2;
static {s2 = "Initialized in static block";}
public static void main(String[] args) {
System.out.println("s1 = " + s1);
System.out.println("s2 = " + s2);
}
}
练习15:
package JAVA5;
public class E15 {
String s;
{ s = "'instance initialization'";}
public E15(){
System.out.println("Default constructor ; s = " + s);
}
public E15(int i ){
System.out.println("int constructor; s = " + s);
}
public static void main(String[] args) {
new E15();
new E15(1);
}
}
练习16:
package JAVA5;
public class E16 {
public static void main(String[] args) {
String sa1[] = new String[4];
sa1[0] = "ni";
sa1[1] = "hao";
sa1[2] = "ya";
for(int i = 0; i < sa1.length; i++)
System.out.println(sa1[i]);
String sa2[] = {"ni","hao","ya"};
for(int i = 0; i < sa2.length; i++)
System.out.println(sa2[i]);
}
}
练习17:
package JAVA5;
class Test{
Test(String s){
System.out.println("1 s = " + s);
}
}
public class E17 {
Test[] array1 = new Test[5];
public static void main(String[] args) {
Test[] array2 = new Test[5];
}
}
练习18:
package JAVA5;
public class E18 {
public static void main(String[] args) {
Test[] array = new Test[5];
for(int i = 0; i <array.length; i++)
array[i] = new Test(Integer.toString(i));
}
}
练习19:
package JAVA5;
public class E19 {
static void printStrings(String... strs){
for(String s:strs)
System.out.println(s);
}
public static void main(String[] args) {
printStrings("these" ,"are","some","strings");
printStrings(new String[]{"these","are","some","strings"});
}
}
练习20:
package JAVA5;
public class E20 {
public static void main(String... args) {
E19.printStrings(args);
}
}
练习21:
package JAVA5;
enum Paper{
ONE,TWO,FIVE,TEN,TWENTY,FIFTY
}
public class E21 {
public static void main(String[] args) {
for(Paper s:Paper.values()){
System.out.println(s + ".ordinal " + s.ordinal());
}
}
}
练习22:
package JAVA5;
public class E22 {
static void describe(Paper pct){
System.out.println(pct + " has a portrait of ");
switch (pct){
case ONE:
System.out.println("1");
break;
case TWO:
System.out.println("2");
break;
case TEN:
System.out.println("10");
break;
case FIVE:
System.out.println("5");
break;
case FIFTY:
System.out.println("50");
break;
case TWENTY:
System.out.println("20");
break;
}
}
public static void main(String[] args) {
for(Paper s: Paper.values())
describe(s);
}
}