package com.xjh.study;
public class IsOdd {
// 判断 i 是否为奇数 (对于负数不生效）
public static boolean isOdd(int i) {
return i % 2 == 1;
}
// 判断 i 是否为奇数
public static boolean isOdd2(int i) {
return i % 2 != 0;
}
}
package com.xjh.study;
import javax.sound.midi.SysexMessage;
import junit.framework.TestCase;
import org.junit.Test;
public class IsOddTest extends TestCase {
public void testIsOdd() {
int a = 0;
assertEquals(false, IsOdd.isOdd(a));
int b = 1;
assertEquals(true, IsOdd.isOdd(b));
int c = 2;
assertEquals(false, IsOdd.isOdd(c));
int d = 3;
assertEquals(true, IsOdd.isOdd(d));
// int e = -1;
// assertEquals(true, IsOdd.isOdd(e));
int f = -2;
assertEquals(false, IsOdd.isOdd(f));
// int j = -3;
// assertEquals(true, IsOdd.isOdd(j));
}
@Test
public void testIsOdd2() {
int a = 0;
assertEquals(false, IsOdd.isOdd2(a));
int b = 1;
assertEquals(true, IsOdd.isOdd2(b));
int c = 2;
assertEquals(false, IsOdd.isOdd2(c));
int d = 3;
assertEquals(true, IsOdd.isOdd2(d));
int e = -1;
assertEquals(true, IsOdd.isOdd2(e));
int f = -2;
assertEquals(false, IsOdd.isOdd2(f));
int j = -3;
assertEquals(true, IsOdd.isOdd2(j));
System.out.println("o");
System.err.println("e");
}
}
package com.xjh.study;
import java.math.BigDecimal;
public class Change {
public static void main(String args[]) {
System.out.println(2.00 - 1.10); // 0.8999999999999999
System.out.printf("%.2f%n", 2.00 - 1.10); // 0.90
System.out.println((200 - 110) + " cents"); // 90 cents
System.out.println(new BigDecimal("2.00").
subtract(new BigDecimal("1.10"))); // 0.90
}
}
package com.xjh.study;
import java.util.ArrayList;
import java.util.List;
public class Elementary {
public static void main(String[] args) {
System.out.println(12345 + 5432l); // 17777
System.out.println(12345 + 5432L); // 17777
// Bad code-uses el(l)as a variable name
List l = new ArrayList();
l.add("Foo");
System.out.println(l); // [Foo]
}
}
package com.xjh.study;
public class JoyOfHex {
public static void main(String[] args) {
System.out.println(
Long.toHexString(0x100000000L + 0xcafebabe));
}
}
package com.xjh.study;
public class LongDivision {
public static void main(String[] args) {
final long MICROS_PER_DAY = 24 * 60 * 60 * 1000 * 1000;
final long MILLIS_PER_DAY = 24 * 60 * 60 * 1000;
System.out.println(MICROS_PER_DAY / MILLIS_PER_DAY); // 5
System.out.println(24 * 60 * 60 * 1000 * 1000); // 500654080 已经溢出了
System.out.println(MICROS_PER_DAY); // 500654080 已经溢出了
System.out.println(MILLIS_PER_DAY); // 86400000
System.out.println(24 * 60 * 60); // 86400
System.out.println("------------------------");
final long MICROS_PER_DAY_2 = 24L * 60 * 60 * 1000 * 1000;
final long MILLIS_PER_DAY_2 = 24L * 60 * 60 * 1000;
System.out.println(MICROS_PER_DAY_2 / MILLIS_PER_DAY_2); // 1000
System.out.println("hello");
System.err.println("a");
}
}
来源 《Java Puzzlers》第二章