Java Coding Tips

Print Map in Java

Arrays.toString(map.entrySet().toArray())

Print List in Java

Arrays.toString(list.toArray())

拼接List的字符串

String.join(‘delimiter’, ListObject)

List<String> list = Arrays.asList("one", "two", "three");
System.out.println("Joined String:" + String.join(",", list));

输出结果为：

System.out.println("Joined String:" + String.join(",", list));

List的数据操作

list.replaceAll(s-> s.toUpperCase())

List<String> list = Arrays.asList("one", "two", "three");
System.out.println("before modification: " + list);
list.replaceAll(s -> s.toUpperCase());
System.out.println("after modification: " + list);

输出结果为：

before modification: [one, two, three]
after modification: [ONE, TWO, THREE]

## 模式匹配

@Test
public void isPositiveInteger() {
    System.out.println("\n*** Positive Intger *****");
    String pattern = "^\\+?[1-9]\\d*"; //? -- {0,1}

    System.out.println("90:" + "90".matches(pattern));
    System.out.println("9:" + "9".matches(pattern));
    System.out.println("90.1:" + "90.1".matches(pattern));
    System.out.println("-9:" + "-9".matches(pattern));
    System.out.println("00:" + "00".matches(pattern));
}

@Test
public void isNegativeInteger() {
    System.out.println("\n*** Negative Intger *****");
    String pattern = "^-[1-9]\\d*";

    System.out.println("90:" + "90".matches(pattern));
    System.out.println("90.1:" + "90.1".matches(pattern));
    System.out.println("-9:" + "-9".matches(pattern));
    System.out.println("00:" + "00".matches(pattern));
    System.out.println("-0.1:" + "00".matches(pattern));
}

@Test
public void isWholeNumber() {
    System.out.println("\n ***  is Pure Number ****");
    String numberPattern = "[+-]?0";

    System.out.println("+0:" + "+0".matches(numberPattern));
    System.out.println("-0:" + "-0".matches(numberPattern));
    System.out.println("0:" + "0".matches(numberPattern));

    //combine three pattern 0, isNegative, isPositive
}

@Test
public void isNegativeDecimal() {
    System.out.println("\n ***  is Negative Number ****");
    String decimalPattern = "^-[0]\\.[1-9]*|^-[1-9]\\d*\\.\\d*";

    System.out.println("-12.1:" + "-12.1".matches(decimalPattern));
    System.out.println("-122:" + "-122".matches(decimalPattern));;
    System.out.println("122:" + "122".matches(decimalPattern));;
    System.out.println("0.2:" + "0.2".matches(decimalPattern));;
}

@Test
public void isPositveDecimal() {
    System.out.println("\n ***  is Positive Number ****");
    String positvePattern = "\\+{0,1}[0]\\.[1-9]*|\\+{0,1}[1-9]\\d*\\.\\d*";

    System.out.println("-12.1:" + "-12.1".matches(positvePattern));
    System.out.println("-122:" + "-122".matches(positvePattern));;
    System.out.println("122:" + "122".matches(positvePattern));;
    System.out.println("0.2:" + "0.2".matches(positvePattern));;
}