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java 字符串

java 字符串

作者: hatlonely | 来源:发表于2020-01-01 18:04 被阅读0次

    java 字符串

    断言

    • startsWith(x): 前缀判断
    • endsWith(x): 后缀判断
    • contains(x): 包含判断
    • equalsIgnoreCase(x): 忽略大小写的判断相等
    assertTrue("stay hungry, stay foolish".startsWith("stay"));
    assertTrue("stay hungry, stay foolish".endsWith("foolish"));
    assertTrue("stay hungry, stay foolish".contains("hungry"));
    assertTrue("hello world".equalsIgnoreCase("Hello world"));
    

    字符串查找

    assertEquals("01234567890123456789".indexOf('6'), 6);
    assertEquals("01234567890123456789".lastIndexOf('6'), 16);
    assertEquals("01234567890123456789".indexOf("678"), 6);
    assertEquals("01234567890123456789".lastIndexOf("678"), 16);
    assertEquals("01234567890123456789".indexOf("abcd"), -1);
    assertEquals("01234567890123456789".charAt(6), '6');
    

    字符串操作

    • substring: 子字符串
    • trim: 去掉前后空白
    • split: 字符串分割成字符串数组
    • join: 字符串合并
    assertEquals("hello" + " " + "java", "hello java");
    assertEquals("HELLO".toLowerCase(), "hello");
    assertEquals("world".toUpperCase(), "WORLD");
    assertEquals(" hello world ".trim(), "hello world");
    assertEquals("0123456789".substring(4), "456789");
    assertEquals("0123456789".substring(3, 6), "345");
    assertEquals("stay hungry, stay foolish".replace("stay", "keep"), "keep hungry, keep foolish");
    assertArrayEquals("java golang swift".split(" "), new String[]{"java", "golang", "swift"});
    assertEquals(String.join("|", new String[]{"java", "golang", "swift"}), "java|golang|swift");
    

    字符串转化

    assertEquals(Integer.parseInt("123456"), 123456);
    assertEquals(Double.parseDouble("123.456"), 123.456, 0.00001);
    assertEquals(Integer.toString(123456), "123456");
    assertEquals(Integer.toHexString(123456), "1e240");
    assertEquals(Double.toString(123.456), "123.456");
    

    字符串构造

    java 的 String 是不可变的,可以通过 StringBuilder(多线程场景下可以使用 StringBuffer) 来构造一个字符串

    StringBuilder sb = new StringBuilder();
    sb.append("hello");
    sb.append(" ");
    sb.append("world");
    sb.append(" ");
    sb.append(123);
    assertEquals(sb.toString(), "hello world 123");
    

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