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String API
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equals
/**
* Compares this string to the specified object. The result is {@code
* true} if and only if the argument is not {@code null} and is a {@code
* String} object that represents the same sequence of characters as this
* object.
* 将此字符串与指定的对象进行比较
* 如果此参数不为null且与指定对象表示的是同一个字符串时，返回结果为true
*
* @param anObject
* The object to compare this {@code String} against
* 参数：要与此字符串对象进行比较的对象
*
* @return {@code true} if the given object represents a {@code String}
* equivalent to this string, {@code false} otherwise
* 返回值：若给定的对象等同于此字符串，则返回true，否则返回false
*
* @see #compareTo(String)
* @see #equalsIgnoreCase(String)
*/
public boolean equals(Object anObject) {
// ==的作用：比较两个对象的引用，引用相同，值一定相同
if (this == anObject) {
return true;
}
// instanceof：判断其左边对象是否为其右边类的实例
// anObject若不是String类的实例，则压根不用比了，直接false
if (anObject instanceof String) {
String anotherString = (String)anObject;// 若是，则先强转Object为String，再参与比较
int n = value.length;// 指定字符串的长度
if (n == anotherString.value.length) {// 长度都不一样，肯定值不同，直接false
// strObj.equals(anObject)
char v1[] = value;// strObj的字符数组
char v2[] = anotherString.value;// anObject的字符数组
int i = 0;
while (n-- != 0) {// 比较2个字符数组相同下标的元素值是否相同
if (v1[i] != v2[i])
return false;
i++;
}
return true;
}
}
return false;
}关于 instanceof 与 getClass()：
instanceof 判断当前左边实例是不是右边类（或右边类的派生类）的实例
getClass 用 == 判断实例类型是否为右边类型
getClass 严格性比 instanceof 要高！
@Test
public void instanceofTest() {
String i = "xws";
System.out.println(i instanceof String);// true
System.out.println(i instanceof Object);// true
}
@Test
public void getClassTest() {
Parent parent = new Parent();
System.out.println(parent.getClass() == Child.class);// false
System.out.println(parent.getClass() == Parent.class);// true
}
class Child extends Parent {
}
class Parent {
}F
G
H
/**
* Returns a hash code for this string. The hash code for a
* {@code String} object is computed as
* <blockquote><pre>
* s[0]*31^(n-1) + s[1]*31^(n-2) + ... + s[n-1]
* </pre></blockquote>
* using {@code int} arithmetic, where {@code s[i]} is the
* <i>i</i>th character of the string, {@code n} is the length of
* the string, and {@code ^} indicates exponentiation.
* (The hash value of the empty string is zero.)
*
* @return a hash code value for this object.
*/
public int hashCode() {
int h = hash;
if (h == 0 && value.length > 0) {
char val[] = value;
for (int i = 0; i < value.length; i++) {
h = 31 * h + val[i];
}
hash = h;
}
return h;
}