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1:String类被final修饰符锁修饰,代表String类一旦声明,就不可被改变;这里的不可变是引用地址不可变,而非指向的内容不可变,下面一张图来理解一下:
再来看一下String类的源码:public final class String implements Serializable, Comparable, CharSequence { private final char[] value; private int hash; private static final long serialVersionUID = -6849794470754667710L; private static final ObjectStreamField[] serialPersistentFields = new ObjectStreamField[0]; public static final Comparator CASE_INSENSITIVE_ORDER = new String.CaseInsensitiveComparator(); public String() { this.value = "".value; } public String(String var1) { this.value = var1.value; this.hash = var1.hash; } 省略....
故被String修饰的类不可被继承;
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