java - contains() 按值比较，而不是引用？

Question

我很惊讶地看到 equals() 显然被 ArrayList<String> 覆盖了。 .因为 Collection<> 中的 contains() 显然是比较值，而不是引用。当然，对于 Collection<Object> , 引用将被比较。在下面的程序中，我不应该在第二行得到 false 吗？

public static void main(String[] args) {
    ArrayList<String> al = new ArrayList<String>();
    al.add("Obama");
    al.add("Reagan");
    al.add("Bush");
    al.add("Nyquist");
    StringBuffer sb = new StringBuffer();
    sb.append("Bush");

    System.out.println("compares values? using constants " + al.contains("Bush"));
    System.out.println("compares values? using local variable " + al.contains(sb.toString()));
}

run:
compares values? using constants true
compares values? using local variable true

Answer 1

Javdaocs for List你是 friend 吗List.contains() 依赖于 .equals():

boolean contains(Object o)
Returns true if this list contains the specified element. More formally, returns true if and only if this list contains at least one element e such that (o==null ? e==null : o.equals(e)).

String.equals()比较 String 的内容(字符):

public boolean equals(Object anObject)
Compares this string to the specified object. The result is true if and only if the argument is not null and is a String object that represents the same sequence of characters as this object.