【题目1】一个ArrayList对象中有若干个字符串元素，现在遍历该ArrayList对象，删除其中所有值为abc的字符串元素。
- 思路：
- 创建类型为String的List集合
- 添加元素
- 遍历集合
- 删除元素
- 注意：正着遍历时，当集合中有连续的abc存在时，会出现删除不干净的情况，需在每次删除后角标自动减一位，或者可以选择倒着遍历。
package leif;
import java.util.ArrayList;
import java.util.List;
public class Test {
public static void main(String[] args) {
List<String> sList = new ArrayList<String>() {
private static final long serialVersionUID = 1L;
{
add("abc");
add("a");
add("abc");
add("b");
add("abc");
add("abc");
add("c");
add("abc");
add("d");
add("abc");
}
};
System.out.println(sList);
for (int i = 0; i < sList.size(); i++) {
if ("abc".equals(sList.get(i))) {
sList.remove(i);
i--;
}
}
System.out.println(sList);
}
}
Java8
package leif;
import java.util.List;
import java.util.stream.Collectors;
import java.util.stream.Stream;
public class Test {
public static void main(String[] args) {
List<String> sList = Stream.of("abc", "a", "abc", "b", "abc", "abc", "c", "abc", "d", "abc").collect(Collectors.toList());
sList.stream().forEach(System.out::println);
sList.stream().filter(s -> !s.equals("abc")).forEach(System.out::println);
}
}
【题目2】取出一个字符串中字母出现的次数，如："abcdekka27qoq"输出格式为a(2)b(1)k(2)。
- 思路：
- 创建Key类型为Character、Value类型为Integer的Map集合
- 遍历字符串
- 判断集合中是否有Key值为当前字符的元素
- 若无，则将当前字符作为Key值存入集合，并将Value值设为1；若有，则取出Key值为当前字符的元素，并将Value值增加1
- 遍历集合，以规定格式输出各元素
package leif;
import java.util.HashMap;
import java.util.Map;
import java.util.Map.Entry;
public class Test {
public static void main(String[] args) {
String s = "abcdekka27qoq";
Map<Character, Integer> cMap = new HashMap<>();
for (char c : s.toCharArray()) {
if (cMap.containsKey(c)) {
cMap.put(c, cMap.get(c) + 1);
} else {
cMap.put(c, +1);
}
}
StringBuffer stringBuffer = new StringBuffer();
for (Entry<Character, Integer> cEntry : cMap.entrySet()) {
stringBuffer.append(cEntry.getKey() + "(" + cEntry.getValue() + ")");
}
System.out.println(stringBuffer);
}
}
Java8
package leif;
import java.util.HashMap;
import java.util.Map;
import java.util.stream.Collectors;
import java.util.stream.Stream;
public class Test {
public static void main(String[] args) {
String s = "abcdekka27qoq";
Map<String, Integer> sMap = new HashMap<String, Integer>() {
private static final long serialVersionUID = 1L;
{
put("index", -1);
}
};
Stream.generate(() -> {
int index = sMap.get("index") + 1;
sMap.put("index", index);
return s.substring(index, index + 1);
}).limit(s.length()).collect(Collectors.groupingBy(letter -> letter, Collectors.counting())).entrySet().stream().forEach(letterEntry -> System.out.print(letterEntry.getKey() + "(" + letterEntry.getValue() + ")"));
}
}
【题目3】编写程序，随机生成5个1~10之间的随机数，存入一个List集合中，编写方法对List集合进行降序排列。
- 思路：
- 创建类型为Integer的List集合
- 生成5个1-10之间的随机数，并存入集合中
- 排序
- 注意：
random.nextInt(10)产生的随机数区间为[0, 10)。
package leif;
import java.util.ArrayList;
import java.util.Comparator;
import java.util.List;
import java.util.Random;
public class Test {
public static void main(String[] args) {
Random random = new Random();
List<Integer> iList = new ArrayList<Integer>() {
private static final long serialVersionUID = 1L;
{
for (int i = 0; i < 5; i++) {
add(random.nextInt(10) + 1);
}
}
};
System.out.println(iList);
iList.sort(new Comparator<Integer>() {
@Override
public int compare(Integer i1, Integer i2) {
return i2 - i1;
}
});
System.out.println(iList);
}
}
Java8
package leif;
import java.util.List;
import java.util.Random;
import java.util.stream.Collectors;
import java.util.stream.Stream;
public class Test {
public static void main(String[] args) {
Random random = new Random();
List<Integer> iList = Stream.generate(() -> random.nextInt(10) + 1).limit(5).collect(Collectors.toList());
System.out.println(iList);
iList.stream().sorted((i1, i2) -> i2 - i1).forEach(System.out::println);
}
}
【题目4】创建俩个散列规则集，求它们的并集、差集和交集。
package leif;
import java.util.HashSet;
import java.util.Set;
public class Test {
public static void main(String[] args) {
Set<Integer> iSet1 = new HashSet<Integer>() {
private static final long serialVersionUID = 1L;
{
add(1);
add(2);
add(3);
add(4);
add(5);
}
};
System.out.println(iSet1);
Set<Integer> iSet2 = new HashSet<Integer>() {
private static final long serialVersionUID = 1L;
{
add(3);
add(4);
add(5);
add(6);
add(7);
}
};
System.out.println(iSet2);
Set<Integer> unionSet = new HashSet<Integer>() {
private static final long serialVersionUID = 1L;
{
addAll(iSet1);
addAll(iSet2);
}
};
System.out.println(unionSet);
Set<Integer> differenceSet = new HashSet<Integer>() {
private static final long serialVersionUID = 1L;
{
addAll(iSet1);
addAll(iSet2);
removeAll(iSet2);
}
};
System.out.println(differenceSet);
Set<Integer> intersectionSet = new HashSet<Integer>() {
private static final long serialVersionUID = 1L;
{
addAll(iSet1);
retainAll(iSet2);
}
};
System.out.println(intersectionSet);
}
}
Java8
package leif;
import java.util.Set;
import java.util.stream.Collectors;
import java.util.stream.Stream;
public class Test {
public static void main(String[] args) {
Set<Integer> iSet1 = Stream.of(1, 2, 3, 4, 5).collect(Collectors.toSet());
System.out.println(iSet1);
Set<Integer> iSet2 = Stream.of(3, 4, 5, 6, 7).collect(Collectors.toSet());
System.out.println(iSet2);
Set<Integer> unionSet = Stream.of(iSet1, iSet2).flatMap(iSet -> iSet.stream()).collect(Collectors.toSet());
System.out.println(unionSet);
Set<Integer> differenceSet = iSet1.stream().filter(i -> !iSet2.contains(i)).collect(Collectors.toSet());
System.out.println(differenceSet);
Set<Integer> intersectionSet = iSet1.stream().filter(i -> iSet2.contains(i)).collect(Collectors.toSet());
System.out.println(intersectionSet);
}
}
【题目5】创建俩个数组线性表，求它们的并集，差集和交集。
package leif;
import java.util.ArrayList;
import java.util.List;
public class Test {
public static void main(String[] args) {
List<Integer> iList1 = new ArrayList<Integer>() {
private static final long serialVersionUID = 1L;
{
add(1);
add(2);
add(3);
add(4);
add(5);
}
};
System.out.println(iList1);
List<Integer> iList2 = new ArrayList<Integer>() {
private static final long serialVersionUID = 1L;
{
add(3);
add(4);
add(5);
add(6);
add(7);
}
};
System.out.println(iList2);
List<Integer> unionList = new ArrayList<Integer>() {
private static final long serialVersionUID = 1L;
{
addAll(iList1);
for (int i : iList2) {
if (!contains(i)) {
add(i);
}
}
}
};
System.out.println(unionList);
List<Integer> differenceList = new ArrayList<Integer>() {
private static final long serialVersionUID = 1L;
{
addAll(iList1);
addAll(iList2);
removeAll(iList2);
}
};
System.out.println(differenceList);
List<Integer> intersectionList = new ArrayList<Integer>() {
private static final long serialVersionUID = 1L;
{
addAll(iList1);
retainAll(iList2);
}
};
System.out.println(intersectionList);
}
}
Java8
package leif;
import java.util.List;
import java.util.stream.Collectors;
import java.util.stream.Stream;
public class Test {
public static void main(String[] args) {
List<Integer> iList1 = Stream.of(1, 2, 3, 4, 5).collect(Collectors.toList());
System.out.println(iList1);
List<Integer> iList2 = Stream.of(3, 4, 5, 6, 7).collect(Collectors.toList());
System.out.println(iList2);
List<Integer> unionList = Stream.of(iList1, iList2.stream().filter(i -> !iList1.contains(i)).collect(Collectors.toList())).flatMap(iList -> iList.stream()).collect(Collectors.toList());
System.out.println(unionList);
List<Integer> differenceList = iList1.stream().filter(i -> !iList2.contains(i)).collect(Collectors.toList());
System.out.println(differenceList);
List<Integer> intersectionList = iList1.stream().filter(i -> iList2.contains(i)).collect(Collectors.toList());
System.out.println(intersectionList);
}
}
【题目6】从文本中读取单词，将所有不重复的单词按升序显示。
package leif;
import java.io.BufferedReader;
import java.io.File;
import java.io.FileReader;
import java.io.IOException;
import java.util.Set;
import java.util.TreeSet;
public class Test {
public static void main(String[] args) {
StringBuilder stringBuilder = new StringBuilder();
try (
FileReader fileReader = new FileReader(new File("C:\\Users\\Administrator\\Desktop\\test.txt"));
BufferedReader bufferedReader = new BufferedReader(fileReader);
) {
String line = "";
while ((line = bufferedReader.readLine()) != null) {
stringBuilder.append(line);
stringBuilder.append("\n");
}
} catch (IOException e) {
e.printStackTrace();
}
Set<String> sSet = new TreeSet<String>() {
private static final long serialVersionUID = 1L;
{
for (String s : stringBuilder.toString().split("\\W")) {
if (!"".equals(s)) {
add(s);
}
}
}
};
System.out.println(sSet);
}
}
Java8
package leif;
import java.io.BufferedReader;
import java.io.File;
import java.io.FileReader;
import java.io.IOException;
import java.util.stream.Collectors;
import java.util.stream.Stream;
public class Test {
public static void main(String[] args) {
StringBuilder stringBuilder = new StringBuilder();
try (
FileReader fileReader = new FileReader(new File("C:\\Users\\Administrator\\Desktop\\test.txt"));
BufferedReader bufferedReader = new BufferedReader(fileReader);
) {
String line = "";
while ((line = bufferedReader.readLine()) != null) {
stringBuilder.append(line);
stringBuilder.append("\n");
}
} catch (IOException e) {
e.printStackTrace();
}
Stream.of(stringBuilder.toString().split("\\W")).filter(s -> !"".equals(s)).collect(Collectors.toSet()).stream().sorted().forEach(s -> System.out.print(s + " "));
}
}
【题目7】从文本中读取单词，将所有单词按升序显示。
package leif;
import java.io.BufferedReader;
import java.io.File;
import java.io.FileReader;
import java.io.IOException;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
public class Test {
public static void main(String[] args) {
StringBuilder stringBuilder = new StringBuilder();
try (
FileReader fileReader = new FileReader(new File("C:\\Users\\Administrator\\Desktop\\test.txt"));
BufferedReader bufferedReader = new BufferedReader(fileReader);
) {
String line = "";
while ((line = bufferedReader.readLine()) != null) {
stringBuilder.append(line);
stringBuilder.append("\n");
}
} catch (IOException e) {
e.printStackTrace();
}
List<String> sList = new ArrayList<String>() {
private static final long serialVersionUID = 1L;
{
for (String s : stringBuilder.toString().split("\\W")) {
if (!"".equals(s)) {
add(s);
}
}
}
};
Collections.sort(sList);
System.out.println(sList);
}
}
Java8
package leif;
import java.io.BufferedReader;
import java.io.File;
import java.io.FileReader;
import java.io.IOException;
import java.util.stream.Collectors;
import java.util.stream.Stream;
public class Test {
public static void main(String[] args) {
StringBuilder stringBuilder = new StringBuilder();
try (
FileReader fileReader = new FileReader(new File("C:\\Users\\Administrator\\Desktop\\test.txt"));
BufferedReader bufferedReader = new BufferedReader(fileReader);
) {
String line = "";
while ((line = bufferedReader.readLine()) != null) {
stringBuilder.append(line);
stringBuilder.append("\n");
}
} catch (IOException e) {
e.printStackTrace();
}
Stream.of(stringBuilder.toString().split("\\W")).filter(s -> !"".equals(s)).collect(Collectors.toList()).stream().sorted().forEach(s -> System.out.print(s + " "));
}
}
【题目8】读取一个java源文件，报告关键字的个数。
package leif;
import java.io.BufferedReader;
import java.io.File;
import java.io.FileReader;
import java.io.IOException;
import java.util.HashMap;
import java.util.Map;
public class Test {
private static final String KEYWORDS = "const, goto, public, protected, private, class, interface, abstract, implements, extends, new, import, package, byte, short, int, long, float, double, char, boolean, void, null, true, false, if, else, while, for, switch, case, default, do, break, continue, return, instanceof, static, final, super, this, native, strictfp, synchronized, transient, volatile, try, catch, finally, throw, throws, enum, assert";
public static void main(String[] args) {
Map<String, Integer> sIMap = new HashMap<String, Integer>() {
private static final long serialVersionUID = 1L;
{
for (String s : KEYWORDS.split(", ")) {
put(s, 0);
}
}
};
System.out.println(sIMap);
StringBuilder stringBuilder = new StringBuilder();
try (
FileReader fileReader = new FileReader(new File("C:\\Users\\Administrator\\Desktop\\test.txt"));
BufferedReader bufferedReader = new BufferedReader(fileReader);
) {
String line = "";
while ((line = bufferedReader.readLine()) != null) {
stringBuilder.append(line);
stringBuilder.append("\n");
}
} catch (IOException e) {
e.printStackTrace();
}
for (String s : stringBuilder.toString().split("\\W")) {
if (sIMap.containsKey(s)) {
sIMap.put(s, sIMap.get(s) + 1);
}
}
System.out.println(sIMap);
}
}
Java8
package leif;
import java.io.BufferedReader;
import java.io.File;
import java.io.FileReader;
import java.io.IOException;
import java.util.Map;
import java.util.stream.Collectors;
import java.util.stream.Stream;
public class Test {
private static final String KEYWORDS = "const, goto, public, protected, private, class, interface, abstract, implements, extends, new, import, package, byte, short, int, long, float, double, char, boolean, void, null, true, false, if, else, while, for, switch, case, default, do, break, continue, return, instanceof, static, final, super, this, native, strictfp, synchronized, transient, volatile, try, catch, finally, throw, throws, enum, assert";
public static void main(String[] args) {
Map<String, Integer> sIMap = Stream.of(KEYWORDS.split(", ")).collect(Collectors.toMap(keyword -> keyword, keyword -> 0));
System.out.println(sIMap);
StringBuilder stringBuilder = new StringBuilder();
try (
FileReader fileReader = new FileReader(new File("C:\\Users\\Administrator\\Desktop\\test.txt"));
BufferedReader bufferedReader = new BufferedReader(fileReader);
) {
String line = "";
while ((line = bufferedReader.readLine()) != null) {
stringBuilder.append(line);
stringBuilder.append("\n");
}
} catch (IOException e) {
e.printStackTrace();
}
Stream.of(stringBuilder.toString().split("\\W")).forEach(s -> {
if (sIMap.containsKey(s)) {
sIMap.put(s, sIMap.get(s) + 1);
}
});
System.out.println(sIMap);
}
}
【题目9】随机生成个数不定个整数，打印频率最高的，如果有俩个一样的最高频率则都输出。
package leif;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;
public class Test {
public static void main(String[] args) {
Map<Integer, Integer> iIMap = new HashMap<Integer, Integer>();
int maxValue = 0;
List<Integer> iList = new ArrayList<Integer>() {
private static final long serialVersionUID = 1L;
{
int number = (int) (Math.random() * 100 + 1);
for (int i = 0; i < number; i++) {
add((int) (Math.random() * 100 + 1));
}
}
};
System.out.println(iList);
for (int i : iList) {
if (iIMap.containsKey(i)) {
iIMap.put(i, iIMap.get(i) + 1);
} else {
iIMap.put(i, 1);
}
maxValue = Math.max(maxValue, iIMap.get(i));
}
for (Entry<Integer, Integer> iIEntry : iIMap.entrySet()) {
if (iIEntry.getValue() == maxValue) {
System.out.println(iIEntry.getKey());
}
}
}
}
Java8
package leif;
import java.util.List;
import java.util.Map.Entry;
import java.util.stream.Collectors;
import java.util.stream.Stream;
public class Test {
public static void main(String[] args) {
List<Integer> iList = Stream.generate(() -> (int) (Math.random() * 100 + 1)).limit((long) (Math.random() * 100 + 1)).collect(Collectors.toList());
System.out.println(iList);
List<Entry<Integer, Long>> iEntryList = iList.stream().collect(Collectors.groupingBy(i -> i, Collectors.counting())).entrySet().stream().sorted(Entry.<Integer, Long>comparingByValue().reversed()).collect(Collectors.toList());
iList = iEntryList.stream().filter(iLEntry -> iLEntry.getValue() == iEntryList.get(0).getValue()).map(iLEntry -> iLEntry.getKey()).collect(Collectors.toList());
System.out.println(iList);
}
}
【题目10】定义一个Point类，包含两个成员变量x和y，分别表示横坐标和纵坐标，随机创建100个点，升序显示这些点。
package leif;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;
import java.util.Random;
import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;
public class Test {
public static void main(String[] args) {
Random random = new Random();
List<Point> pointList = new ArrayList<Point>() {
private static final long serialVersionUID = 1L;
{
for (int i = 1; i <= 100; i++) {
add(new Point(random.nextInt(100), random.nextInt(100)));
}
}
};
System.out.println(pointList);
Collections.sort(pointList, new Comparator<Point>() {
@Override
public int compare(Point point1, Point point2) {
int i = point1.getX() - point2.getX();
if (i == 0) {
return point1.getY() - point2.getY();
} else {
return i;
}
}
});
System.out.println(pointList);
}
}
@Data
@NoArgsConstructor
@AllArgsConstructor
class Point {
private int x;
private int y;
}
Java8
package leif;
import java.util.List;
import java.util.Random;
import java.util.stream.Collectors;
import java.util.stream.Stream;
import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;
public class Test {
public static void main(String[] args) {
Random random = new Random();
List<Point> pointList = Stream.generate(() -> new Point(random.nextInt(100), random.nextInt(100))).limit(100).collect(Collectors.toList());
System.out.println(pointList);
pointList = pointList.stream().sorted((Point point1, Point point2) -> point1.getX() - point2.getX() == 0 ? point1.getY() - point2.getY() : point1.getX() - point2.getX()).collect(Collectors.toList());
System.out.println(pointList);
}
}
@Data
@NoArgsConstructor
@AllArgsConstructor
class Point {
private int x;
private int y;
}
