Mutable members should not be stored or returned directly

╰+哭是因爲堅強的太久メ 2023-10-03 14:21 32阅读 0赞

Mutable objects are those whose state can be changed. For instance, an array is mutable, but a String is not. ***Mutable class members should never be returned to a caller or accepted and stored directly***. Doing so leaves you vulnerable to unexpected changes in your class state.

Instead use an unmodifiable `Collection` (via `Collections.unmodifiableCollection`, `Collections.unmodifiableList`, …) or make a copy of the mutable object, and store or return the copy instead.

This rule checks that arrays, collections and Dates are not stored or returned directly

**Noncompliant Code Example:**

class A {
        
      private String [] strings;
    
      public A () {
        
        strings = new String[]{
        "first", "second"};
      }
    
      public String [] getStrings() {
        
        return strings; // Noncompliant
      }
    
      public void setStrings(String [] strings) {
        
        this.strings = strings;  // Noncompliant （按此规则，构造器也不应该这样做）
      }
    }
    
    public class B {
        
    
      private A a = new A();  // At this point a.strings = {"first", "second"};
    
      public void wreakHavoc() {
        
        a.getStrings()[0] = "yellow";  // a.strings = {"yellow", "second"};
      }
    }

**Compliant Solution:**

class A {
        
      private String [] strings;
    
      public A () {
        
        strings = new String[]{
        "first", "second"};
      }
    
      public String [] getStrings() {
        
        return strings.clone();
      }
    
      public void setStrings(String [] strings) {
        
        this.strings = strings.clone();
      }
    }
    
    public class B {
        
    
      private A a = new A();  // At this point a.strings = {"first", "second"};
    
      public void wreakHavoc() {
        
        a.getStrings()[0] = "yellow";  // a.strings = {"first", "second"};
      }
    }