例外
// 例外処理
class MyException extends Exception {
public MyException(String s){
super(s);
}
}
public class MyApp{
public static void div(int a, int b){
try {
if (b < 0){
throw new MyException("not minus!");
}
System.out.println(a / b);
} catch (ArithmeticException e){
System.err.println(e.getMessage());
} catch (MyException e){
System.err.println(e.getMessage());
} finally{
System.out.println(" -- end -- ");
}
}
public static void main(String[] args){
div(3, 0);
div(5, -2);
}
}
ラッパークラス
public class MyApp{
public static void main(String[] args){
// Integer i = new Integer(32);
// int n = i.intValue();
Integer i = 32; // auto boxing
i = null;
int n = i; // auto unboxing
System.out.println();
}
}
generics:型の汎用化
class MyData<T> {
public void getThree(T x){
System.out.println(x);
System.out.println(x);
System.out.println(x);
}
}
public class MyApp{
public static void main(String[] args){
// MyInteger mi = new MyInteger();
// mi.getThree(55);
MyData<Integer> i = new MyData<>();
i.getThree(32);
MyData<String> s = new MyData<>();
s.getThree("hello");
}
}
Thread処理:
class MyRunnable implements Runnable{
@Override
public void run(){
for (int i= 0; i < 500; i++){
System.out.print('*');
}
}
}
public class MyApp{
public static void main(String[] args){
MyRunnable r = new MyRunnable();
Thread t = new Thread(r);
t.start();
for (int i= 0; i < 500; i++){
System.out.print('.');
}
}
}
無名クラス
public class MyApp{
public static void main(String[] args){
// MyRunnable r = new MyRunnable();
// Thread t = new Thread(r);
// t.start();
new Thread(new Runnable(){
@Override
public void run(){
for (int i= 0; i < 500; i++){
System.out.print('*');
}
}
}).start(); // 無名クラス
for (int i= 0; i < 500; i++){
System.out.print('.');
}
}
}
Stringクラス
public class MyApp{
public static void main(String[] args){
String s = "abcdef";
System.out.print(s.length());
System.out.print(s.substring(2, 5));
System.out.print(s.replaceAll("ab","AB"));
String s1 = "ab";
String s2 = "ab";
if (s1.equals(s2)){
System.out.print("same!");
}
if (s1 == s2){
System.out.print("same!same!");
}
}
}
printfメソッド
public class MyApp{
public static void main(String[] args){
int score=50;
double height=165.8;
String name ="yoshimoto";
System.out.printf("name: %s, score: %d, height: %f\n", name, score, height);
System.out.printf("name: %-10s, score: %10d, height: %5.2f\n", name, score, height);
String s = String.format("name: %10s, score: %-10d, height: %5.2f\n", name, score, height);
System.out.println(s);
}
}
Math, randomクラス
import java.util.Random;
public class MyApp{
public static void main(String[] args){
double d = 53.234;
System.out.println(Math.ceil(d));
System.out.println(Math.floor(d));
System.out.println(Math.round(d));
System.out.println(Math.PI);
Random r = new Random();
System.out.println(r.nextDouble()); // 0-1
System.out.println(r.nextInt(100)); // 0-1
System.out.println(r.nextBoolean()); // 0-1
}
}
ArrayList
import java.util.*;
public class MyApp{
public static void main(String[] args){
List sales = new ArrayList<>();
sales.add(10);
sales.add(20);
sales.add(30);
for (int i = 0; i < sales.size(); i++){
System.out.println(sales.get(i));
}
sales.set(0, 100);
sales.remove(2);
for (Integer sale: sales){
System.out.println(sale);
}
}
}
Hash.set
import java.util.*;
public class MyApp{
public static void main(String[] args){
HashSet sales = new HashSet<>();
sales.add(10);
sales.add(20);
sales.add(30);
sales.add(10);
System.out.println(sales.size());
for (Integer sale: sales){
System.out.println(sale);
}
sales.remove(30);
for (Integer sale: sales){
System.out.println(sale);
}
}
}
