java面试-内存分配与回收策略

/**
 * -Xms20M -Xmx20M -Xmn10M -XX:+PrintGCDetails -XX:SurvivorRatio=8
 */
public class TestAllocation {

    private static final int _1MB = 1024 * 1024;

    public static void testAllocation() {
        byte[] allocation1, allocation2, allocation3, allocation4;
        allocation1 = new byte[2 * _1MB];
        allocation2 = new byte[2 * _1MB];
        allocation3 = new byte[2 * _1MB];
        allocation4 = new byte[4 * _1MB];
    }

    public static void main(String[] args) {
        testAllocation();
    }
}

/**
 * -verbose:gc -Xms20M -Xmx20M -Xmn10M -XX:+PrintGCDetails -XX:SurvivorRatio=8 -XX:PretenureSizeThreshold=3145728
 */
public class TestPretenureSizeThreshold {
    private static final int _1MB = 1024 * 1024;

    public static void testPretenureSizeThreshold() {
        byte[] allocation;
        allocation = new byte[4 * _1MB];  //直接分配在老年代中
    }

    public static void main(String[] args) {
        testPretenureSizeThreshold();
    }
}　　

 *-Xms20M -Xmx20M -Xmn10M -XX:+PrintGCDetails -XX:SurvivorRatio=8 -XX:MaxTenuringThreshold=1
 */
public class TestTenuringThreshold {
    private static final int _1MB = 1024 * 1024;

    public static void testTenuringThreshold() {
        byte[] allocation1, allocation2, allocation3;
        allocation1 = new byte[_1MB / 4]; //256k内存，survivor空间可以容纳
        allocation2 = new byte[4 * _1MB];
        allocation3 = new byte[4 * _1MB];
        allocation3 = null;
        allocation3 = new byte[4 * _1MB];
    }

    public static void main(String[] args) {
        testTenuringThreshold();
    }
}