JVM——内存泄漏与内存溢出

public class HandlerDemoActivity extends Activity implements OnClickListener {
  private static final int MESSAGE_INCRESE = 0;
  private static final int MESSAGE_DECRESE = 1;
  private TextView tv_demo_number;
  private Button btn_demo_increase;
  private Button btn_demo_decrease;
  private Button btn_demo_pause;
  private Handler handler = new Handler(){
     //回调方法
     public void handleMessage(android.os.Message msg) {
       String strNum = tv_demo_number.getText().toString();
       //转换为整型数据,获取当前显示的数值
       int num = Integer.parseInt(strNum);
       switch(msg.what){
       case MESSAGE_INCRESE:
          num++;
          tv_demo_number.setText(num + "");
          if(num == 20){
            Toast.makeText(HandlerDemoActivity.this, "已达到最大值", 0).show();
            btn_demo_pause.setEnabled(false);
            return;
          }
          //发送延迟的+1的消息
          sendEmptyMessageDelayed(MESSAGE_INCRESE, 300);//指的是延迟处理，而不是延迟发送
          break;
       case MESSAGE_DECRESE:
          num--;
          tv_demo_number.setText(num + "");
          if(num == 0){
            Toast.makeText(HandlerDemoActivity.this, "已达到最小值", 0).show();
            btn_demo_pause.setEnabled(false);
            return;
          }
          //发送延迟的-1的消息
          sendEmptyMessageDelayed(MESSAGE_DECRESE, 300);//指的是延迟处理，而不是延迟发送
          break;
       }
     }
  };
  @Override
  protected void onCreate(Bundle savedInstanceState) {
     super.onCreate(savedInstanceState);
     setContentView(R.layout.activity_handler_demo);
     init();
  }
  private void init() {
     tv_demo_number = (TextView) findViewById(R.id.tv_demo_number);
     btn_demo_increase = (Button) findViewById(R.id.btn_demo_increase);
     btn_demo_decrease = (Button) findViewById(R.id.btn_demo_decrease);
     btn_demo_pause = (Button) findViewById(R.id.btn_demo_pause);
     btn_demo_increase.setOnClickListener(this);
     btn_demo_decrease.setOnClickListener(this);
     btn_demo_pause.setOnClickListener(this);
  }
  @Override
  public void onClick(View v) {
     ....
  }
}

举例1：
/**
 * 演示内存泄漏
*
 * @author FLY
 * @create 14:43
 */
public class ChangeHashCode {
public static void main(String[] args) {
        HashSet set = new HashSet();
        Person p1 = new Person(1001, "AA");
        Person p2 = new Person(1002, "BB");
        set.add(p1);
        set.add(p2);
        p1.name = "CC";
        set.remove(p1);
        System.out.println(set);//2个对象！
//        set.add(new Person(1001, "CC"));
//        System.out.println(set);
//        set.add(new Person(1001, "AA"));
//        System.out.println(set);
}
}
class Person {
int id;
    String name;
public Person(int id, String name) {
this.id = id;
this.name = name;
    }
@Override
public boolean equals(Object o) {
if (this == o) return true;
if (!(o instanceof Person)) return false;
        Person person = (Person) o;
if (id != person.id) return false;
return name != null ? name.equals(person.name) : person.name == null;
    }
@Override
public int hashCode() {
int result = id;
        result = 31 * result + (name != null ? name.hashCode() : 0);
return result;
    }
@Override
public String toString() {
return "Person{" +
"id=" + id +
", name='" + name + '\'' +
'}';
    }
}
举例2:
/**
 * 演示内存泄漏
 * @author FLY
 * @create 14:47
 */
public class ChangeHashCode1 {
public static void main(String[] args) {
        HashSet hs = new HashSet();
        Point cc = new Point();
        cc.setX(10);//hashCode = 41
hs.add(cc);
        cc.setX(20);//hashCode = 51
System.out.println("hs.remove = " + hs.remove(cc));//false
hs.add(cc);
        System.out.println("hs.size = " + hs.size());//size = 2
}
}
class Point {
int x;
public int getX() {
return x;
    }
public void setX(int x) {
this.x = x;
    }
@Override
public int hashCode() {
final int prime = 31;
int result = 1;
        result = prime * result + x;
return result;
    }
@Override
public boolean equals(Object obj) {
if (this == obj) return true;
if (obj == null) return false;
if (getClass() != obj.getClass()) return false;
        Point other = (Point) obj;
if (x != other.x) return false;
return true;
    }
}

/**
 * 演示内存泄漏
*
 * @author FLY
 * @create 14:53
 */
public class MapTest {
static Map wMap = new WeakHashMap();
static Map map = new HashMap();
public static void main(String[] args) {
init();
testWeakHashMap();
testHashMap();
    }
public static void init() {
        String ref1 = new String("obejct1");
        String ref2 = new String("obejct2");
        String ref3 = new String("obejct3");
        String ref4 = new String("obejct4");
wMap.put(ref1, "cacheObject1");
wMap.put(ref2, "cacheObject2");
map.put(ref3, "cacheObject3");
map.put(ref4, "cacheObject4");
        System.out.println("String引用ref1，ref2，ref3，ref4 消失");
    }
public static void testWeakHashMap() {
        System.out.println("WeakHashMap GC之前");
for (Object o : wMap.entrySet()) {
            System.out.println(o);
        }
try {
            System.gc();
            TimeUnit.SECONDS.sleep(5);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println("WeakHashMap GC之后");
for (Object o : wMap.entrySet()) {
            System.out.println(o);
        }
    }
public static void testHashMap() {
        System.out.println("HashMap GC之前");
for (Object o : map.entrySet()) {
            System.out.println(o);
        }
try {
            System.gc();
            TimeUnit.SECONDS.sleep(5);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println("HashMap GC之后");
for (Object o : map.entrySet()) {
            System.out.println(o);
        }
    }
}
/**
 * 结果
* String引用ref1，ref2，ref3，ref4 消失
* WeakHashMap GC之前
* obejct2=cacheObject2
 * obejct1=cacheObject1
 * WeakHashMap GC之后
* HashMap GC之前
* obejct4=cacheObject4
 * obejct3=cacheObject3
 * Disconnected from the target VM, address: '127.0.0.1:51628', transport: 'socket'
 * HashMap GC之后
* obejct4=cacheObject4
 * obejct3=cacheObject3
 **/