JDK 源码分析

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76. `String`

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package com.diguage.truman;

public class StringUtils {
  public static String switchFormat(int cur, int length) {
    String str = "" + cur;
    int q = length - str.length();
    switch (q) {
      case 0:
        break;
      case 1:
        str = "0" + str;
        break;
      case 2:
        str = "00" + str;
        break;
      case 3:
        str = "000" + str;
        break;
      case 4:
        str = "0000" + str;
        break;
      case 5:
        str = "00000" + str;
        break;
      case 6:
        str = "000000" + str;
        break;
      default:
        break;
    }
    return str;
  }

  public static String format(int cur, int len) {
    return String.format("%0" + len + "d", cur);
  }
}

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package com.diguage.truman;

import org.openjdk.jmh.annotations.*;

import java.util.concurrent.TimeUnit;

import static com.diguage.truman.StringUtils.format;
import static com.diguage.truman.StringUtils.switchFormat;

@BenchmarkMode(Mode.Throughput)
@Measurement(iterations = 10, time = 30)
@OutputTimeUnit(TimeUnit.SECONDS)
@Warmup(iterations = 3, time = 5)
@State(Scope.Thread)
public class StringUtilTest {

  // TODO 怎么书写测试用例？
  @Param({"1", "2"})
  int num;

  private static final int[] lens = {1, 2, 3, 4, 5, 6, 7};

  @Benchmark
  public String testStringFormat() {
    return format(num, num);
  }

  @Benchmark
  public String testSwitchFormat() {
    return switchFormat(num, num);
  }
}

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package com.diguage.truman;

import org.junit.jupiter.api.Test;

import java.util.*;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.LockSupport;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

import static org.assertj.core.api.Assertions.assertThatThrownBy;

public class StringTest {


  @Test
  public void testDedup() {
    List<String> lists = new ArrayList<>(1);
    for (int i = 0; i < Integer.MAX_VALUE; i++) {
      String is = String.valueOf(i);
      String s1 = "D瓜哥 · https://www.digauge.com".repeat(i % 10) + is;
      lists.add(new String(s1.substring(0, s1.length() - is.length())));
      String s2 = i + "D瓜哥 · https://www.digauge.com";
      lists.add(new String(s2.substring(is.length())));
      System.out.println(lists.size());
      if (i % 1000 == 0) {
        LockSupport.parkNanos(TimeUnit.SECONDS.toNanos(2L));
      }
    }
  }

  @Test
  public void testSplit() {
    String s = "abc";
    System.out.println(Arrays.toString(s.split("\\|")));


    // 调用 split 方法，如果参数为 null 时，则抛异常
    assertThatThrownBy(() -> s.split(null)).isInstanceOf(NullPointerException.class);
  }

  @Test
  public void testReplaceAll() {
    String value = "${abc} 是一个占位符，${abc}";
    Set<String> placeholders = getAllPlaceholders(value);

    for (String placeholder : placeholders) {
      System.out.println(value.replaceAll(placeholder, "ABC"));
    }
  }

  /**
   * 占位符正则表达式：${\w*}
   */
  private static final Pattern PH_PATTERN = Pattern.compile("(\\u0024\\{\\w*\\})+");

  private static Set<String> getAllPlaceholders(String value) {
    Matcher matcher = PH_PATTERN.matcher(value);
    Set<String> placeholders = new HashSet<>();
    int matcherStart = 0;
    while (matcher.find(matcherStart)) {
      String group = matcher.group();
      placeholders.add(group);
      matcherStart = matcher.end();
    }
    System.out.println(Arrays.toString(placeholders.toArray(new String[0])));
    return placeholders;
  }

}

JDK 源码分析

友情支持

76. String

76. `String`