Java的String源码解析

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java的属性

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private final char value[];  //final类型的char数组，则赋值之后是不能改变的。

   /** Cache the hash code for the string */
   private int hash; // Default to 0 //哈希值

   /** use serialVersionUID from JDK 1.0.2 for interoperability */
   private static final long serialVersionUID = -6849794470754667710L;

常用的构造函数

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//默认给一个空间
 public String() {
        this.value = new char[0];
    }
    
  public String(String original) {
        this.value = original.value;
        this.hash = original.hash;
    }    
    //支持char数组初始化
    public String(char value[]) {
        this.value = Arrays.copyOf(value, value.length);
    }  
    //支持StringBuilder初始化
    public String(StringBuilder builder) {
        this.value = Arrays.copyOf(builder.getValue(), builder.length());
    }

常用到的函数

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//返回char数组中对应的字符
  public char charAt(int index) {
        if ((index < 0) || (index >= value.length)) {
            throw new StringIndexOutOfBoundsException(index);
        }
        return value[index];
    }
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//输入一个String返回一个char数组
    public char[] toCharArray() {
        // Cannot use Arrays.copyOf because of class initialization order issues
        char result[] = new char[value.length];
        System.arraycopy(value, 0, result, 0, value.length);
        return result;
    }

附上java中考到的一个算法题。

求String字符串中重复的字符算法题

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public static Map<Character, Integer> allTotalSum(String str) {

	char[] chars=str.toCharArray();//把String转换成char数组
	
	HashMap<Character, Integer> hash = new HashMap<Character, Integer>();

	for (int i = 0; i < chars.length; i++) {
		if (!hash.containsKey(chars[i])) {
			hash.put(chars[i], 1);
		} else {
			int count = hash.get(chars[i]) + 1;
			hash.put(chars[i], count);
		}
	}
	return hash;
}