1 需求

1.1 Field Summary

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1.2 Constructor Summary

• public String() : 空构造
• public String(byte[] bytes) : 把字节数组转成字符串
• public String(byte[] bytes,int index, int length) : 把字节数组的一部分转成字符串
• public String(char[] value) : 把字符数组转成字符串
• public String(char[] value,int index, int count) : 把字符数组的一部分转成字符串

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1.3 Method Summary

• 判断字符串是否为空
  • public boolean isEmpty()
• 获取字符串的长度
  • public int length()
• 判断字符串是否相等
  • public boolean equals(Object anObject)
  • public boolean contentEquals(StringBuffer sb)
  • public boolean contentEquals(CharSequence cs)
  • public boolean equalsIgnoreCase(String anotherString)
• 判断是否包含子字符串
  • public boolean contains(CharSequence s)
  • public boolean matches(String regex)
• ……
  • public boolean startsWith(String prefix, int toffset)
  • public boolean startsWith(String prefix)
• ……
  • public boolean endsWith(String suffix)
     
• 分割字符串
  • public String[] split(String regex)
  • public String[] split(String regex, int limit)
• ……
  • public int indexOf(int ch)
  • public int indexOf(int ch, int fromIndex)
  • public int indexOf(String str)
  • public int indexOf(String str, int fromIndex)
• 判断某个字符最后出现的位置
  • public int lastIndexOf(int ch)
  • public int lastIndexOf(int ch, int fromIndex)
  • public int lastIndexOf(String str)
  • public int lastIndexOf(String str, int fromIndex)
• 字符串替换
  • public String replace(char oldChar, char newChar)
  • public String replace(CharSequence target, CharSequence replacement)
  • public String replaceFirst(String regex, String replacement)
  • public String replaceAll(String regex, String replacement)
• 字符串查找
  • public String substring(int beginIndex)
  • public String substring(int beginIndex, int endIndex)
  • public CharSequence subSequence(int beginIndex, int endIndex)

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2 接口

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3.X 示例：字符串定义（两种方式）

public class Test {
    public static void main(String[] args) {
        String s1 = "hello";
        String s2 = new String("hello");

        System.out.println(s1 == s2);
    }
}

参考资料

JAVA字符串的两种定义方式的区别_java中字符串的定义方式及区别-CSDN博客

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3.X 示例：未初始化报错

public class Test {
    public static void main(String[] args) {
        String s1;

        System.out.println(s1);
    }
}

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3.X 示例：空字符串

public class Test {
    public static void main(String[] args) {
        String s1 = "";
        System.out.println(s1.isEmpty());
        System.out.println(s1.length());
    }
}

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3.X 示例：null字符串

public class Test {
    public static void main(String[] args) {
        String s1 = null;
        System.out.println(s1.isEmpty());
    }
}

public class Test {
    public static void main(String[] args) {
        String s1 = null;
        System.out.println(s1.length());
    }
}

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4 参考资料

java基础-String_public string{byte[] bytes,-CSDN博客